512 MONTHLY WEATHER REVIEW. NOVEMBER, 1907
Budapest. Obsematoire sismique.
Dellenbaugh, Frederick 8.
Great Britain. Meteorological ofice.
Rapport annuel sur les observetoires sismiques des pays de la Sainte
Couronne de Hongrie. Budapest. 1907. 11 p. 8 O .
The romance of the Colorado river. xxxv, 399 p. RO.
Hourly readings obtained from the self-recording instruments at four observatories in connection with the Meteorological office,
1906. London. siii, 197 p. fo.
Herault. Commission rn6tborologique. Bulletin mbtborologique. Ann68 1906. Montpellier 1907. 128 1'. 4O.
Hesse. Gmsehersogliche hydrographische Bureau. Deiitsches meteorologisches Jahrbuch . . .1906. Darmstadt. 1907.
Hoyt, John Clayton and Grover, Nathan Clifford. River discharge. New York. 1907. vii, 137 p. 8O.
Milham, Willis I. Cloud classiflcation. 9 p. 8O. Williamstown. 1907.
Riefler, 8. Die Uhrenanlage der Hauptstation fiir Erdbebenforschung aiu physi-
kalischen Staatslaboratorium zu Hamburg. Laibach. 1907. 12 p. 8O.
RHUENT PAPERS BEARING ON METEOROLOGY.
H. H. KIMBALL. Librarian.
[13], 59 p. fO.
~~~
The subjoined titles have been selected from the contents
of the periodicals and serials recently received in the Library
of the Weather Bureau. The titles selected are of papers or
other communications bearing on meteorology or cognate
branches of science. This is not a complete index of the
meteorological contents of all the journals from which it has
been compiled; it shows only the articles that appear to the
compiler likely to be of particular interest in connection with
the work of the Weather Bureau. Unsigned articles are indi-
cated by a -
American eociety of civil engineera. Pw.eetEin!is. New I'ork. 1 1 . 3 i. Dec.,
1007.
Bruyn-Kops, J. de. Notes 011 rainfall at Savannah, Ga. p.
1101-1110. [Includes tabulation of all cases o f cumsire rainfall
at Savannah, Ga., 1889-1906, inclusive.]
- Lightning protection. p. 1083-1084. [Describes recent forms
of lightning arrestors.]
Woosnam, R. B. Ruwmzori ancl its life zones. 11.616 639.
[Iucludes notes on the climate.]
- Experiments on wind pressure. p. 139-140. [Abstract of paper
by T. E. Stanton.]
Schuster, Arthur. The diurnal variation of terrestrial magnetism. p. 80-88.
W[ilkinson], A. Air resistance. [Abstract oP article by ~ToUl~et.]
p. 567.
B[orns], H. Indian Ocean meteorology and the southwest mon- soon. [Abstract of article by C. TV. Brebner.] p. 590.
- Preventing frost on show windows. Colrl - weather advice.
p. 375.
- Electric waves in the service of meteorology. [Abstract of paper by Guillen-Garcia describes the use of thunderstorm re-
corclers in forecasting.] p. 382-383.
Stentzel, Arthur. Its effect on the habit- ability of the planet.
Tatin, Victor. Les oiseaus. leh abroplanes et le coefficient de la resistance de l'air. p 309-312.
,Soubies, Jacques. Physiologic de l'aeronaute. p. 316-317. [AL- stract.]
- L'argon de Yair atiuosphbrique. p. 9. [Note on new method of extracting argon ancl the other rare gases of the atmosphere.]
Trovato-Castorina, (3. Sur la direction des decharges Blectrique+ atmobphkriques dans le9 coups de foudre. p. 928. [Abstract.]
Jaerisch, Paul. Zur Theorie der Luftdruck8chwankringt.n allf
Grund der hydrodpaniischen (;leichungen in aphlri.;chc.n Koordi-
naten. p. 481-498.
Teisserenc de Bod, Leon. Ueber dei Verteilung der Temperatiir
in der Atmosphlre am nerdlichen Polarkreis unrl in Trappeh. 11. 498-499.
Eleclricrrl uiorld. Neic York. 19. 60. Dec. 7 , 1:/(t;.
Geographical journal. London. v. 50. Dec.. 1907,
Nature. London. v. 77. Dec. 12, l %t ;.
Royal society. PrOCadin38. London. Series A. v. SYJ. No. A 596.
Science abstracts. London. v. 10. Nov., 1.90;.
Scientajic Amencan suppkment. New Ilork. v. 64. Pec. 24, 1:w.
The climate of Mars.
1'. 383.
Atrophile. Pm-is. 15 cinii6e. Noit., 1907.
Ntiture. Ptirk 36 an&. 14 die.. 13117. Supplmiient.
Joi~mal de phyctique. Paris. 4 8Prie. Toine 6. Nov., 1907.
b f ~o l o g i e c h s Zeiiachrift. Braunachioeig. Bd. 24. Nov. 1907.
Hann, J. M. E. Stephan iiber Temperatur, Regen und Winde von Marseille. p. 500-501.
Hann, J. Die aquivalente Temperatur als klimatischer Faktor. p. 601-504.
Trabert, Wilhelm. Eine mijgliche Ursache der geringen Tem- peraturabnahme in grossen Hijhen. p. 504-506.
Nippoldt, A. VorlaiiAge Ergebnisse der magnetischen Landes- aufnahme von Baden, Hessen und Elsass-Lothringen. p. 506-508.
Hann, J. Osc. V. Johansson : Ueber die auemometrischen Wind-
stlrkemessuugen in Finland. p. 508-509.
Hann, J. R.Strachan iiber die Temperatur urn die brltischen
Inseln in Beziehung zum Golfstrome.
H[ann], J. A. Defant iiber den Talwind des Unterinntales. p. 511.
Schmidt, Wilhelm. Ueber Messungen der terrestrischen Re-
fraktion auf dem hohen Sonnblick.
Macdowall, Alex. B. Sonnenflecken und Regenfall zu Rothesay
(Schottland) 1804 bis 1904. p. 514.
Hann, J. Der tLgliche Gang der Temperatur in den Vereinfgten Stailten. p. 514515.
H[ann], J. Zum Klima von Porto Rim. p. 515-516.
- Dr. L. Grossman iiber die Veriinderlichkeit der Temperatur von
Tag zu Tag an der deutschen Kiiste 189c1899.
Exner, F. M. TV. N. Shaws Untersuchungen uber die Lebens-
geschiclite ron Luftstrijniungen an der Erdoberfllche. p. 520-523.
H[&nn], J. Zum Iilima von Finnland. p. 523.
Messerschitt, J. B. Die crste Generalversammlung der inter-
nationalen scisiuologischeii dssoziation im Hmg VOIII 21. Lis 25.
SepteiulJer 1907. 11.636-626.
Pctermnnno Miltedungen. Gotha. 53. Band, 1307.
Halbfass, -. Apparat ron Bchnitzlein zur selbsttAti,oen Auf-
zeichnung von Wasserstiindeu. p. 341-248.
Physikali~che Zeztschrift. Leipzig. S Jahrgang. 15 Noa. 1307.
Linke, F. UelJer die Arbeiten des Samoa-Observatoriunis. p. 871.
Bornstein, I1. Zur Gesuhichte der hundertteiligen Thermometer-
skala. p. 871-874. [Inversion of the Celsius scale attributed to
Lime.]
Herrmann, E. Uelrrr tatsiicliliche vieltlgige Perioden des Luft-
p. 509-511.
p. 518-514.
p. 516-518.
N~~luru~iesenachnftliche Rundachau. Berlin. 22 Jahrgang. .5 De=., l l j 7 .
drackes. p. 874-879.
Zritnchrift fiir Inatriciiit,ntenkun~l(,. Berlin. 2: Jahrgaiig. Nov., 1307.
SDrung, A. Eine Vereinfacliang des Gallenkamrxjchen Rwen-
-AuffaG&apparates. p. 3-1&343. -
lingen en ,iiwhande.lingen. No. 1/12.
19OK 8 p.
-
Nclherl~t.nh. Koninklijk Nederlnnclnch meteorolvgbch Inn~titic?ct. Mededee-
Galle, P. H. Cyclone in the Arabian Sea. October 1Y-Noveulber 4,
Lo Surdo, Antonino. I1 nuovo metodo cli Buut Augstrijm por lo
Societa degli epettroecgisti italicmi. Mwiorie. Calania. v. 36. 1307.
studio della radiazione solare. p. 193-197. [Abstract.]
~~~
STUDIES OF FROST AND ICE CRYSTALS.
BY W m S o ~ 4. BENTLEY. Dated Jericho. Vt., May ZS, 1906. RevLad July, 1%~;.
(Contin.wd from October Reviezo.)
~III.-CLASSIFI(l.4TION OF ICE CRYSTALS.
(67) List c f t p e s .
There are at least five different and characteristic types among the nuclear or germ ice crystals, and two or three
additional post-nuclear types. In general, i f growth is al-
lowed to proceed for a sufficient length of time, each of these
various germ types passes thru certain typical and character-
istic growth phases peculiar to it. All, or nearly all, when
first organized, -possess smooth edges ancl contours, but they
subsequently pass thru the scalloped, the ray, and the branch-
like stages of growth before completion. These various types,
because of peculiarities of form and resemblance to the objects
after which they are named, may be grouped and named as
follows:
1. Lanceolate . . . . . . . . . . . Lance-like, MLI.
2. Discoidal . . . . . . . . . . . . . Disc-like, MDB.
3. Solid hexagonal . . . . . .Solid hexagonal plate-likca, XIHC.
4. Flower-like . . . . . . . . . . . Ice flower-fonu,MFD.
6. Coralline.. . . . . . . . . . . . .Resembling coral, RICF.
. . . .Resembling a spandrel, IISE.
Each of these respective types requires and will receive especial
mention by itself in the text, in the order of relative frequency
of occurrelice of each in nature, so far as I have observed them
at .Jericho, Vt.
' (G S ) Tcype Jf LA. Latinrolat+> ice o-!ystols.
These lance-like or needle-like crystals are illustrated in
NOVEMBER, 1907. MONTHLY WEATHER REVIEW. 513
photographs Nos. 233 and 234. Some of the crystals are very
long and slender and lance-like, others shorter and broader a t
the center than a t the extremities, while still others broaden
out so greatly a t a central point along one of their edges as
to suggest the idea that segments of disks had attached them-
selves to them. Perhaps those firet mentioned occur most
frequently. They usually form upon and shoot outward from
some object, as from the edges and sides of ponds, brooks,
and artificial receptacles holding water in process of freezing.
Photographs Nos. 283 and 235 will convey an idea of their
general aspect.
The very first ice crystals to form when water begins to
freeze are almost invariably of this description. As these lat-
ter grow upon the surface, scallops and branches form ancl
grow outward from one or both edges, as shown in photo-
graphs Nos. 235, 236, 237, and 288; and eventually grow in
parallel rows downward into the water from their under sides,
ili the manner shown in photographs Nos. 239 A and 239 B.
They are perhaps the main fabrics of the ice, as they alone
merge and form ice films by themselves in addition to fre-
quently combining with other types of ice crystals to form such
films. The needle-like ice crystals that liroaden out upon one
edge at the center (see photograph No. 231) always form in-
dependent of a support in the free water, and proceed to grow
in many cases in the manner shown in photograph No. 240,
thru the formation of scallops around their edges. These
scallops soon develop into rays and branches, and they pass
into the branch-like state and continue their growth in a
branch-like manner.
(6.9) Type XDB. Biscoidal ice rrystals
These strange and most interesting crystals of ice come
into visible existence in the form of tiny, round, thin, disks of
ice of various dimensions, as &own in the photograph No.
241. Some seem to be perfectly fiat, ancl others slightly con-
cave. All are exceedingly thin, and when first formed look
like tiny films or specks of oil resting upon the surface of the
water. They vary somewhat one from another in size and
form, and in the degree of perfection, or spheroidicity, of the
disks. Ofttimes two or more crystals merge together while
yet in the germ state and form many-lobed disks of irregular,
unsymmetrical shapes. At this first stage discoidal crystals
seem not to possess secondary ases and grow in a round and
seemingly most uncrystal-like manner. But as mrowth pro-
greases they soon come to the parting of the ways , and grow
differently. A t this, their critical stage of growth, tiny scal-
lops begin to form at certain equidistant points (six in nuill-
ber) around their edges. Photograph No. 242 shows them a t
this stage of growth. This is a most strange and fascinating
period in their life history. Under the influence of continued
cold and a more rapid rate of growth and of certain mysterious
crystallic laws, seemingly latent influences become active, and
they pass from the germ, or nuclear, into tho mature, from the
simple into the complex state of being; they acquire seconcl-
ary axes, and grow afterward in a more truly crystal-like man-
ner, and are more in accord with the hexagonal system of crys-
tallization to which they belong. Scallops soon form around
their whole circumference and grow rapidly larger, but those
that first appeared grow much faster than the others. Photo-
graph No. 243 shows them at this period of their growth.
Eventually certain of the scallops push outward so far beyond
the others as to gite a star-like or flower-like appearance to
the crystals, and they pass into the beautiful ice flower
stage shown in photographs Nos. 2-14 and 245.
The nest step consists in a marvelously rapid development
of the six longer scallops or rays, which push outward far
beyond the others and assume the role of primary rays; then
follows the formation and growth of numerous secondary rays
upon and around such primary rays. The beautiful appearance
3 1
of such flower-shaped crystals, or  ice flowers , is well shown
in photographs Nos. 246 and 247.
The final and last step in their development consists in a
continuation of the growth of the main rays and the formation,
or multiplication and growth of secondary rays thereon. This
stage is well shown in the beautiful branch-like crystals por-
trayed in photographs Nos. 218, 249. The crystals attain
their greatest beauty and complexity a t this point, and such
as may have developed apart by themselves and in a symmet-
rical manner, often possess a beauty and complexity of form
and outline rivaling that of many of the branch-like snow
cq-stals which they so greatly resemlile.
(70 ) T y p MHC. SiJlid he.ra~prin1 ice crystuls.
Ice crystals of this form differ little from those last men-
tioned, except that they possess hexagonal forms, having sharp
or but slightly rounded corners instead of circular forms and
outlines as is the case with discoidal crystals. Examples of
this and other types of crystals may be seen in photographs
Nos. 241 and 250. They pass successively thru the scallop, the
ray, and the branch-like states of growth as do the latter, but
unlike them, begin and conduct their whole growth from the
very first upon the hesagonal plan, upon and around secondary
axes, in a manner similar to that of the snow crystals. Owing
to crowding and early merging together individual ice crys-
tals of this, ancl indeed of other descriptions. are rarely per-
mitted under natural conditions to continue development for
any considerable length of time in a perfectly symmetrical
manner or to attain a very considerable size. But under arti-
ficial conditions, such as may be brought about in the case of
ice crystals that are allowed to form and to grow upon the
calm surface of the water (as in a pail of water in process of
freezing), individual crystals of this and of other types can
lie kept apart from each other and allowed to grow by t,hem-
selves, by removing any crystals that form or float into their
iinmediste vicinity. Under such favorable conditions, they
can be inarle to grow and develop into crystals of large size,
and of great beauty, complexity, and s p m e t r y of foriii.
( 7 1 ) Tiipe MFD. Floirvr-1il.e iw crystals.
This type of ice crystal seems to begin at once in the liexs-
gonal star or flower forin. These are quite tiny a t first, and of
simple form, the usual germ form consisting of a tiny hesagonal
star with six leaf-like petals, like the smaller crystals shown
in photographs Nos. 250 and 251. They rarely remain long in
this form. Scallops and secondary branches soon form upon
and around the edges of each of the six primary petals and
they pass into the branch-like stage, as shown in photographs
Nos. 252 ancl 253. This type of crystal also assumes elegant
and symmetrical branching forms if allowed to develop under
favorable artificial or natural conditions.
(72) Type XSE. &iniirlrelliforni ice crystals.
These singular ice crystals vary somewhat in form one from
auother, even when first organized. Commonly one edge is
straight in contour, ancl the opposite one curving. The two
edges often conspire to outline a hat-shaped or spandrel-like
figure. Photograph No. 254 pictures a typical example.
These strange forms, like other types, successively pass thru
the scallop and the branch-like stages of growth. Photograph
No. 255 shows thein while in the scallop stage, and No. 266
pictures one after entering upon the branch-like stage.
Singularly enough, quite a few of these and also some crys-
tals of the needle-form type, shown in photograph No. 234,
grow outward from the corners toward the straight edge, and
amiime a horseshoe or meniscus-like form. Photograph No.
2-57 shows a spandrelliform crystal that developed in this
strange manner, while No. 258 shows a needle-form crystal,
and also the spandrelliform crystal at a later stage of growth,
after it had grown in the manner just described. Why certain
514 MONTHLY WEATHER REVIEW. NOVEMBER, 1907
isolated crystals of these respective types grow in the strange
abnormal manner shown in the photographs is indeed most
mysterious; and the mystery is heightened by the fact that it
often happens that crystals of both of the respective types
under consideration form and grow in a normal manner a t the
same time and upon the same body of water as those that
develop abnormally.
(78) Type Jf CF. Coralline ice crystals.
This graceful and elegant type of ice crystal usually, if not
invariably, forms upon and grows out from some preconsti-
tutad nucleus, as from some one or more of the other types, or
from some irregular discoidal crystal germ. I n general the
coralline crystals seem rarely to grow from mature discoidal,
hexagonal, or flower-shaped crystals; they seem to prefer
the needle or lance-form ice crystals, or the spandrelliform
crystals, as nuclei from which to develop. Coralline ice
crystals consist of myriads of rounded, convoluted, disk-
like oukgrowths, clustered one outside another in such a
manner as to form graceful curving branches, greatly re-
sembling certain forms of coral. Their whole developnient
occurs in a sinuous and meandering, rather than a straight
and regular fashion, and in this regard they resemble the
meandering type of window-ice crystals. Why these coral forms
should grow in this seemingly uncrystal-like manner, upon
the surface of water supporting growing needle-like, flower-
like, and hexagonal ice crystals side by side with them, all of
them growing in a crystal-like manner markedly unlike the
coral forms, is indeed most strange and incomprehensible.
Beautiful spncimens of this type of ice crystal may be seen in
photographe Nos. 259 and 260. No. 259 formed and grew
from a tiny twin discoidal crystal similar to the one seen at
one side of the coral-form ice crystal.
(76) ddditioiiul photographs of i c p crystnls.
The authors collection of photographs of ice crystals num-
bers over 200 and contains many beautiful and interesting
forms, in addition to those already mentioned. It is thought
best to select a few from among them to use for illustrative
purposes. These added ones are Nos. 261, 862, 263, 264, and
265. No. 261 shows an interesting specimen of a twin discoidal
ice crystal a t a second stage; two circular discoidal crystals
united together to produceit. No. 262 shows a very interest-
ing group of ice crystals of various types. It shows how ice
crystals of various types, sizes, etc., form and grow at the same
time, side by side, upon a given body of calni, freezing water.
No. 263 is a photograph of a lenticular body of ice formed
by the freezing of water in a shallow dish. I n this case the
water was frozen rapidly, and the ice crystals that accom-
plished the work formed around the edges of the dish and
grew inward; hence the so-called air tubes within the ice, in-
stead of forming with their longer radii normal to the surface
of the water, formed for the most part parallel to the surface
of the water. The forms and arrangement of the air tubes
within this lens-shaped body of ice are well shown in the photo-
graph.
Nos 264 and 265 show how environment and crowding im-
pair symmetrical growth, and how the segments of neighbor-
ing crystals lying farthest apart froin such crystals as may be
in their vicinity are Rtimulated in their growth by the pros-
imity of relatively large areas of crystal-free spaces of chilled
water surface, from which to draw material for new growth,
while those segments that lie nearest adjoining crystals are
retarded and hindered in their growth by such contiguity,
and by a consequent lack of extensive areas of chilled surface
water (water molecules) in their immediate vicinity from which
to draw material for growth. They serve to establish the fact
that growing ice crystals, resting upon the surface of the
water, a t first draw but little from beneath the surface of
the water to aid in their growth; but that they draw material
for their growth almost wholly from a thin film of chilled sur-
face water.
1X.-HAIL.
(75) Probable manner qf formation and classijfcdion.
It is well known that as a result of the action of certain
meteorological forces and conditions, not yet well understood
in all cases, a portion of the raindrops formed in summer dur-
ing rain and thundershowers and tornadoes, and also in winter
by the melting of snow crystals or snowflakes, is sometimes
frozen in the air or in the clouds and converted into solid
masses or accretions of ice called hail. In general, the forms,
structures, sizes, degree of transparency or opacity, and pre-
sumable manner of origin of hailstones formed in winter vary in
considerable degree from those produced in summer. Because
of this, and also because in general winter hail is peculiarly
the product of general snowstorms and of horizontal air cur-
rents, whereas summer hail is peculiarly the product of local
rain and thundershowers and of violently ascending air cur-
rents, it is convenient and advisable to separate hailstones
into two classes, winter hail and summer hail, according to
the respective times of occurrence and manner of origin.
(76) Carise atid occiirreiict ?f irtinter hail.
Because of its apparently greater relative frequency of occur-
rence, winter hail should perhaps receive mention first.
I n general, winter hail is peculiarly the product of the
eastern or southeastern segments of wiclespead general storms.
Such storm segments seem to produce hail not always, but only
in some cases. Whenever winter hail occurs the melting of
the snow crystals, which presumably go to its upbuilding, is
due to the presence of a warm but presumably relatively thin
and somewhat elevated stratum of air lying between the earth
and the clouds or between two low cloud strata. Such warm
air currents almost certainly come from the south or east and
flow spirally inward in a horizontal manner toward the centers
of such storms between the colder air strata existing within
such storms both above and below them. The melted snow
that descends as liquid raindrops from the lower side of a
warm air current freezes into hail while the drops are falling
thru the cold substratum of air lying between the warm stratum
and the earth.
Winter hail ofttimes occurs siiiiultaneously over relatively
large areas. I n general, sleet or mist sleet and rain precede
and follow the occurrence of winter hail. Such hail usually
occurs during southeast winds, when the temperature of the
air at the earths surface ranges from 23 to 35 F. The
individual winter hailstonefa, tho occasionally of practically
uniform size, in general vary somewhat in size and sphericity,
both during a given storm and from one stornl to another.
Hailstones varying from one-thirtieth inch to one-eighth inch
often fall together.
($7 ) Striictriw atid -forms tzf rcinter hnilstoties.
The interior structure of winter hailstones varies somewhat
in different cases. All possess tiny air tubes and air bubbles,
but some in greater quantity than others. Some contain but
a few relatively large ones, others many small ones. Some-
times a tiny group of bubbles occurs clustered within their
nuclear portions. In general, the larger air tubes radiate
from the center outward. I n most cases the majority of the
air tubes are clustered a t the center of each hailstone.
The great majority
are round, but some are egg-shaped, and pear-like shapes are
not rare. These latter are of much interest. Pear-shaped
hailstones are doubtless due to the fact that the larger spher-
oidal ones, because of their greater weight, fall downward
faster than the smaller hailstones and the smaller undercooled
raindrops, and hence overtake and merge with these. In
some cases the tiny raindrops encountered are not too much
undercooled to have time to spread around considerably upon
Winter hailstones assume various forms.
NOVEMBER, 1907. 515
the hailstones before solidification takes place; but in others
they are undercooled to such an extent as to freeze instantly
upon impact. The latter cases presumably produce the pear-
shaped hailstones.
The writer secured many interesting photographs of winter
hailstones, and of sections of such stones, during the winter
of 1906-7, a few of which are reproduced herein as illustra-
tions. Nos. 267 B, 268 A, 268 B, 270, and 271 show the typical
arrangement of the air tubes within the stones. No. 266B
shows a more diffuse and less common arrangement. Nos.
267 A, 268 A, and 269 A show whole pear-shaped hailstones,
while 267 B, 268 B, and 269 B show sections of pear-shaped
and oval-shaped stones under larger magnifications.
(7s) Ocritrrence and cause of sionnier linil.
Summer hail seems to be peculiarly a product of violent
summer showers, and especially of thundershowers and torna-
does and of violently expanding volumes of cloud-laden air.
Newly formed or forming showers, or newly forming annexes
to old ones, and those terrible rotating storms called tornadoes
seem to be the principal, if not the only summer storms that
produce hail. Unlike winter hail, summer hail occurs over
very small areas and is a purely local phenomenon. Yet it
frequently happens that hail occurs simultaneously, or on the
same date, at various and perhaps widely separated points.
Hence it may be presumed that in general the same peculiar
causes that operate to produce hail within some particular
shower of a series will operate at other points, and cause the
formation of hail there also. In general the portion or seg-
ment of a given shower that produces hail is of relatively
small area, hence the path of a hailstorm is quite narrow.
Such hailstorm paths vary from perhaps a few hundred feet
to as much, in some cases, as a mile or so in breadth. It
seems to be the case usually, if not invariably, that the clouds
extend to a very great height above the particular segment
of a shower that produces hail. Probably in most cases such
hail-producing clouds far overtop the surrounding clouds that
produce rain only.
(79) rsirnl striirtiire of si~niniw Aaalstones.
Tho the individual summer hailstones occurring in the
same or in different individual storins often vary markedly
one from another in size and exterior form, yet in general their
internal structures and appearances are quite characteristic
and similar. The nuclei of most summer hailstones consist of
whitish, more or less opaque and seemingly amorphous ice.
In nearly all cases a coat of clear normal ice extends around
and incloses the opaque nucleus, and, in the case of most large
hailstones, many alternate coats or accretions of both clear and
partly opaque amorphous ice seem to have been superimposed
in alternate concentric order upon and around such nuclei.
Because of this a cross section of a large hailstone presents a
circular banded appearance. A great majority of the smaller
summer hailstones are round, ovoidal, or pyramidal in shape.
The larger ones are remarkably less regular in form than the
smaller ones, and a larger percentage of these possess ovoidal,
oblate, or irregular jagged forms. Small summer hailstones
rarely merge or freeze together, but when, as usually happens,
small and large ones occur together, the small ones frequently
merge with the large ones and freeze in most varied order
upon them.
(SO) Pacziliar shiictzwes.
Certain peculiar large egg-shaped and facetted hailstones
possess such a post-nuclear structure as would seem naturally
to suggest that the outer or post-nuclear portion was formed
subsequent to the nucleus, as .z result of the merging of many
small hailstones. The absence of cavities within them, how-
ever, makes this theory of their origin untenable. Under the
microscope the whitish, snow-like, nuclear ice and the concen-
tric coats of post-nuclear ice are seen to be thickly threaded
by air tubes chaotically arranged, by icy nodules, and by
granular fibers resembling those of which granular amorphous
snow is composed, or such as would likely result were the
fibers partially melted. The forms, locations, and arrangements
of these interior air tubes and of the other features that
resemble nodules and fibers of granular amorphous snow, cor-
respond so closely to the jagged granules and fibers of which
actual natural granular amorphous snow is composed, as to
leave little doubt but that they have such a snow origin, and
were inclosed and eventually frozen within a liquid coating
of ice-cold water surrounding a pellet of granular snow, all of
which may be said to constitute a raindrop of melted snow .
(S I ) Probable manner of forniation of siimnier hail.
Assuming this to be the case, hailstorms not only have a
granular snow origin, but as growth progresses in cloudland
they must repeatedly and alternately encounter clouds of
warm mist and cold snow. If we may judge of the origin and
formation of summer liailstones by what seems to be revealed
or indicated by their forms, size, structure, etc., then i t would
seem that they are, in general, formed in the manner described
in the following paragraphs:
(a ) The nuclei, or rather what eventually go to form such
nuclei, are first organized in the form of pyramidal or star-
shaped granular snow, within the central and upper portions
of very lofty, violently and vertically expanding, mushrooru-
shaped cumulus, or cumulo-cirrus clouds. The rapidly as-
cending air currents within the central portions of such clouds
may expand upward in some cases as internal whirlwinds, and
in others very strongly but without marked rotary motion; but
their upward motion is assumed to be so rapid as to enable
them to sustain and carry along upward with them all the
raindrops and granular snow that come within their grasp.
The pellets of granular snow are blown upward and expelled
or released from the grasp of the powerful updraft air currents
only a t or near the suiiimit and spreading portion of a cloud.
Once the pellets reach the spreading-out portion of a cloud,
they are blown outward in a horizontal, rather than upward in
a vertical manner; thus they lose their ascensional motion and
begin to fall earthward. The larger pellets and the larger
hailstones, caused by melting and refreezing necessarily fall
first and nearest to the central vortex, while the smaller pellets
are blown farther outward into the spreading portion of the
clouds, and fall earthward farther away from the center. Many
of the latter eventually fall as rain completely to earth at some
point beneath the shower clouds.
(6) A portion of the granular pellets, however, and especially
the large ones such as fall closest to the central vortex, as
they fall earthward and become partly melted a t lower levels,
encounter strong horizontal indraft air currents, and are
drawn by them again into the shower vortex, and are again
carried far upward and converted into ice, and recoated with
granular snow, and eventually expelled again, as in the first in-
stance, from the summit and spreading portions of the shower
clouds. In some cases, as when the uprushing and whirling
winds of the showers central vortex are very swift, the hail-
stones may even once again undergo a descent and an ascent,
as in the first and second instances. Or again, in their fall
earthward they may encounter a secondary, newly-forming
vortex, as an annex to the main one; and after being partly
melted within its milder air, they may be carried far upward
by it, again reaching cold, freezing altitudes and be once again
frozen, before they become so heavy as finally to fall to earth.
In short, this theory assumes that, in general, summer hail-
stones begin as granular snow, and are melted or partly
melted only by partial descent, and are congealed only thru
The author assures us that he arrived at this theory quite indepen-
dently of suggestions from the very limited authorities and literature to
which he had aCCeS i.-EDITOR.
______________
516 MONTHLY WEATHER REVIEW. NOVEMBER, 1907
ascent within the clouds. The writer believes that the process
of hail formation as herein described, or some modification of
it, is capable of completely explaining all the various plie-
nomena of summer hail. Surely powerful air currents or winds
must blow upward thru and within hail-producing cloucls to
sustain and buoy up the larger hailstones for the length of
time necessary for them to grow to SO considerable a size.
[To be continued.]
THE WINDS OF THE LAKE REGION.
~
By Prof. Ar.hnhu J. I I ~N H I , United ht.Ltes Weather Bureau. Rated Deelillber 10, iyni.
All motions of the air depend directly or indirectly upon
differences in temperature. Differences in temperature arise
in several ways, mostly, however, as a result of the varying
amount of solar energy received a t the earths surface in tlie
various latitudes and the unequal heating of land and water
surfaces. The temperature of the equatorial regions, for
reasons that need not here be stated, is high as compared with
that of the polar regions; as a consequence the isobaric sur-
faces are inclined toward the poles, ani1 there is, therefore, a
flow of the upper air from the equatorial regions polewarcl in
both hemispheres, with a countercurrent in the lower air from
the poles toward the equator. This interchanging motion
between the equatorial and the polar regions is modified by
the deflecting force of the earths rotation, by differences in
barometric pressure on different parallels of latitude, and l y
other causes which conspire to interrupt ancl at times reverse
the general motions here indicated.
In the Northern Hemisphere, with which we are most con-
cerned, the principal winds are (1) the northeast trades whose
polar limits do not extend much above 30 north latitude, and
(2) the prevailing westerly winds of the middle latitudes.
Each of these winds forms an elemental part of the general
circulation of the atmosphere, and is therefore controlled and
moclified by general rather than local influences.
The normal temperature gradient between the equator ancl
the poles near the surface of the earth is the principal cause
of the winds. It is subject to a rather large annual inequal-
ity-that is to say, it is strongefit in winter and weakest in SUIU-
mer-conseclucntly the winds, particularly of the miclclle lati-
tudes, also show an annual inequality both in direction and
velocity; and, moreover, they are interrupted by local and
temporary disturbances in temperature which produce gradi-
ents strong enough to overcome the normal gradient for the
time and place. These local and temporary disturbances occur
most frequently in the warm season, when the equatorial-
polar gradient is weakest; hence it follows that the winds are
most variable in summer and steadiest in winter. Another
cause for the general seasonal changes in the force and direc-
tion of the wind is the annual migration of the heat equator.
The temperature differences which arise between the continents
and the oceans, as a result of such migration, cause a corres-
ponding movenient of the lower portions of the atmosphere
from the colder to the warmer region.
The meteorological stations in the Lake region from which
the material for the following remarks was obtained are of two
classes, viz, (1) the cooperative stations at which the prevail-
ing direction of the wind by eye observations is recorded each
day, and (2) the regular stations of the Weather Bureau where
the direction ancl force of the wind is automatically recorded
thruout each of the twenty-four hours. The Weather Bureau
stations, with but one exception, are stationed along the Great
Lakes. Since the direction of the wind is controlled at times
by temperature differences that arise between contiguous sur-
faces of land ancl water, the local winds at lake stations may
not always show the general moyement of the air, but merely
the direction and movement of the air within a narrow zone
surrounding the lake. To meet this objection use has been
made of a number of cooperative stations situated a t some
distance from the lakes.
Winds of the cold season.-In the cold season, viz, from
November to March, the winds of the Great Lakes are con-
trolled chiefly l ~y the meteorological conditions which prevail
in the interior of the continent. The general drift of the
surface winds in the United States east of the Rocky Moun-
tains and north of about the thirty-fifth parallel of latitude
for this period is from a westerly quarter; more specifically,
the winds of the upper Missouri Valley, the upper Mississippi
Talley, and the northern portion of the upper Lake region
are north]! est; in the southern part of the upper Lake region,
the lower Lake regiou, and the Ohio Valley, west or southwest,
and in the Middle Atlantic Statew, northwest. The mean path
of the prevailing winds  in these regions in winter is shown
in tig. 1, No. 1.
As the Iiieridional altitude of the sun increases, the thermal
conditions which prevailed over the continent in winter be-
come reversed; the interior becomes warmer than the oceans
on the saiue parallels of latitude on both the east and west
coasts and the Gulf of Mexico on the south. The consequence
is, aH pointed out by Ferrel, the air orer the interior of the
continent becomeH more rare than over the oceans, rises and
flows out in all tlirections above; while the barometric pres-
sure is diminislied, and there is an inflow below from all sides
to take its place. The effect of this general warming up is not
sufficiently strong, however, completely to overcome and re-
verse the generally eastward drift of the atmosphere in them
latitudes, but i t is suficiently powerful when the pressure
gradients are weak to control the direction of the minds; hence,
in the transit,ory months of spring and early summer the winds
co~ue alternately under the influence of (1 ) steep temperature
and pressure gradients caused by the lingering cold of the
continental interior, and (2) increasing solar radiation. The
effect of the latter is seen mainly during intervals of clear
weather and diminishing winds, which follow the passage of
an area of high pressure and cold weather. As a consequence
the winds of spring are more lariable than those of winter, as
may be seen from fig. 1, No. 2, where are clmrted the prevail-
ing winds of spring.
An interesting fact in connection with the winds of spring
is the beginning of what appears to be a slight monsoon in-
fluence on Lake Michigan, viz, onshore ninds from April to
September of each year, due in part, i t is believed, to the dif-
ference of temperature which prevails between the lake sur-
face and contiguous land surfaces, ancl in part to the prevail-
ing pressure distribution in the late spring months.
The prevailing winds on the Houthwest shore of the lake, as
may be seen from the data for Chicago, Table 1, are northeast
froiii April to September; on the west shore, as at Milwaukee,
northeast for April and May, and southeast from June to
August, or from the lake to the land in both cases. A t Esca-
nabs, on Green Bay, the prevailing winds are northerly until
May, then southerly from May to October, both inclusive.
The prevailing winds at C h n d Haven, the only available sta-
tion on the east shore, are easterly in April and southwesterly
from May to September, with, however, a large percentage of
northwesterly winds in July and August. Thus it will be seen
1 The term ** prevailing  unfortunately does not afford auy indication of the relative frequency of the winds so designated. IP the wiud blew
an equal number of times from each of the eight principal points of the
compass, it would be said to have no prevailing direction, there beiug
13.5 per ceut from each direction. If, on the other hand, it had blown
as much as 13 per cent from any direction, that direction would be deeig-
nated as the prevailing one. The term * prevailing  may, therefore,
indicate winds of frequency ranging between 13 and 100 per cent. In
Table 1 is given the percentage of wind from each of the eight principal
points of the cornpas.: as determined hourly by automatically recording
instruments.
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1 See A Popular Treatise on the Winds .