OCTOBER, 1896. MONTHLY WEATHER REVIEW. 373
have tried to explain, by analysis, t h e production of the five images observed by me, but was obliged to give it up on account of the com- plexity of the calculations. I n the case of three images, Bravais also shows how only certain arts of an object can produce multiple images; this phenomenon actual& occurs as we have seen above.
Finally, if we reflect that two layers of air of very different densi- ties cannot remain for a long tinie superposed one upon t h e other
without becoming mixed, we shall understand the instability of the phenomenon and why the fata morgana and the mirage on cold water
can succeed each other so rapidly i n the same part of the lake.
An excellent description of the fata niorgana as seen froiii
Reggio, on the Italian coast, when looking toward Messins
across the Straits of Messina, is given by Mascart irr the third
volume of his Treatise on Optics, Paris, 1893. I n this volume
(pages 305-835) he also gives a complete elucidation of tlie
optical principles involved in every forin of mirage, including
even the triple images of vessels in the distant horizon, the
multiple images observed by ArtLgo and Biot, and every form
of fatn morgana. Mascarts formula seems to us applicable
to a11 the cases enumerated in the above qnotations.
AN mEELIMENTBL RAINFBLL.
A letter of Julie 20 from Prof. L. Errera, of Brussels, is
published in Ciel et Terw for August., 1S96, S V I I , 11. 353,
giving the following description of an experimental study
into the formation of cloads, which wiI1, we hope, attract the
attention of physicists who are conducting advanced courses
in meteorology in Aiiiericaii colleges and universities. The
esperimen t has been repeated at the Weather Burmu with
success, hit i t should tie carried out on a large scale, with a
very tall jar and great care as to uniformity of temperature,
if one desires to get satisfactory results. Probably the cluuds
can be photographed by using a flash light and with care in
the illumination. Other liquids, sncli as ether, benzine, tur-
pentine, and water, should also be tried :
Take a cylindrical vase of bohemian glass of about 20 centinieters in height and 12 in diameter and till it half full of strong alcohol-92 per
cent-and cover it with a porcelain saucer and warm i t over the water bath. I t is necessary to warm it up for quite a long time, in order that
the liquid and the whole vase and the Iiorcelain cover may attain a high temperature and be in tlieriual equililiriun~ among themselves, but without bringing the alcohol to t h e boiling point. Remove the
whole from the warm place and, being careful not to agitate the liquicl, The warm
liquicl continues to sen(] up an a~iunc~ance of alcoliolic vapors. After .8ome niinutes the porcelain cover is sufficiently cooled so that these
vapors commence to coiidense in ita immediate neighborhood. S o ~n there are thus fornieil clearly visible cloucls, and these in their turn resolve themselves into very fine droplets of rain, which fall steadily,
vertically, and in countless numbers into the liquid. The droplets, when measurecl by means of a horizontal microscope, have mi aver:ige diameter of from 40 to 50 thousandths of a millimeter; they are some- times larger but more frequently smaller. This interesting spectacle
may last for half an how. A t first the vapors rise quite up to t h e porcelain cover, but in propor- tion as the Whole system cools down the level where the condensacion occurs naturally lowers more and more, ani1 now we find a perfectly
clear zone above the zone of cluuds. We have i n this way i n minia-
ture the whole aqueous circulation of the atmosphere; the eval~ornting liquid represents the ocean, far above it the cuoling porcelnin saucer is
the pure sky, below this the cloutls, which resolve themselves into real
water, and the latter returns to the ocean. Except that in phce uf water everything is niatle of alcohol.
I t would be surprising if this simple phenomenon has never been
described before; but as you s:ly that you do not remeniber to have seen an account of this anywhere in the nieteorological literature, with which you are so perfectly familinr, I think it well to explain tlie con- ditions under which the phenomena are pro(1iiced.
[The experiments here described by Errera may be co~upared with t h e well-known siniilar work of Tynclall antl Aitken, especially those
described bv the well-known physicist of Edinburgh in his memoir entitled Oh dust, fogs, and clouds. (Eclinb. Transactions, lSSO-Sl,
S S X .) But Aitken makes use of complicated apparatus, while the experiments of Errera can he repeated a t any time and in the simplest
manner. Moreover, Errera describes very interesting phenomena that Aitken did not perceive, or, a t least, lias passell over in silence. Tyndall considers an analogous subject in his note On the formation
and henomena of clouds. (Roy. Soc. LlJIldOIl Proceedings, 1S69,
ilace the vase upon a wooden table and observe it carefully.
X V I E ~A . L ANCASTER.]
Possibly this experiment may serve to explain some meteorological problems that are still under discussion; for example, whether the production of rain is necessarily subordinated to electrical influences,
as is acknowledged by Clement Ley and many other authors. Our experiment is, moreover, susceptible of several variations. After having taken the vase from the warn1 bath, if we replace the
warm porcelain cover by a colt1 one the differences of temperature be- tlteen different points of the system become greater and the phe- noniena are esaggerated; little whirlwintls, which are true squalls, are proilucecl. When the alcohol is still very warm and if, l)y acci- dent, t h e vase is a little wariiier on one sitle than 011 the other, in that
portion which is above t h e level of the liquitl we see the alcoholic vapor performing a regular rotstion nliout a horizontal axis; it con- tinually rises along the warmer side of the vase and tlescends alon the c(di1er side. The proof that this rotation is due to the cause that f Rupgest is, that in order tal reverse the Ilirection of the rotation it suf-
fices t u cool the side of the vase along which the vapclrs are rising and this is easily done by the application of a strip uf filter paper wet with
cold water and frequently renewed.
A t first tliduglit the formation of cloncl and rain in Erreras
esprriment where there can br no dust particles to serve as
nuclei for coiidensatio~i, seems to be cuntrary to Mr. Aitkens
theory and esperinieiits, according to which all ordinary
rains and clouds depend npon the preseuce of dnet nuclei ;
hiit there is really no contrndiction. Rhen air is cooled to a
temperature near dew point, conderisation hegins where i t is
most easily possible, viz : firbt, on hygroscopic surf:tces and
nest to this, on sinall particles of dust, iiinny of which are
also hygroscopic and, finally, on those that are smallest, eveii
though they I_re not specially hygroscopic. If cooling pro-
ceeded orily thus far, we should have dew, fog, and cloud, but
no rain. If the process of cooling still continue then a cer-
tain critical stage is passed over and the aqueous molecules
begin to agglomerate without waiting for the presence of
nuclei; t>hey conie together in larger drops and IJY a more
violent process. The extent to which cooling must proceed
in order that this foriii of coudensation may begiii has been
investigated, a d may be defined as follows : If the cooliiig
is produced by espansion, then the aniouii t of expansion
requirecl in order to produce the secund stage of condensation
is 1.255 tiiiies the expalision necessary to produce the first stage
of CuIii~enS~tiOli. (See bIUNTHLY \YEATHER KEVIEW, hhy,
1SO6, page 167.) As long ago :is 1S4l Espy (see his Philos-
upliy of Storms, page 35) observed the fact that when, by
espniisioii, we determine the dew-point for n iiiasa of air
coiitained within a gliiss jar, several tiiiirs in succeseioii, the
dew-point seeins to be steadily rising.
On coni ming together the experiments matle on dry air, there
appeared t u t little ciiscrepancy, 1mt witli moist air tliis w m nut so, nlltl
I was iniluceil to institute a set of exl~eriments to see whether length
of time had any inflrience on t h e rebiilt. I, therefore, performed a great number of experiments siniilur in a l l respects, except the length of time which intervened between the time uf pumping air intu the
ne~~helescope and u; letting it out, anti, to niv abtunishment, I found the rise of the mercury, after the tlisclr:irge, ;wnstantly greater as the time was lunger, tip to about t\+rlvtt ur fifteen clays; but beyonll that
time the effect did nlIt seen) to be incrrnsetl. I t f d l l J \w from these experiments that when air saturate11 nitli v:tpor is confinetl in a glass
vessel, air-tight, and cnntaining :t small portiun of \\.:iter, it will cease to be saturated to the aniount of four or five degrees in the dew-point
in fifteen days. Whatever may be the caiibe of this remarkable fact, so cuntrary to all I J U ~ notions, since the experiments of Dalton on the subject of the ilew-point, the followillg tnlJle uf experiments proves
beyund all doubt that it is a fact. Dues water or glass so attract the Iwticles of aqueous vapor as to cun(1ense sume of these particles on them antl lirinp cluwn the dew-point foiir or five tlegreeu I,t.low the
temperature of the water and of the air inc.lucler1 in the vessel?
The Editor can not clouht that Professor Espy W ~A here iii
presence of the pIieiioiiieli(~ii that has sul~seqiie~i tly been
inyestigated by Barus mid C. T. R. \\ilson. Bj7 allowitig his
air to stand so long i t had, by wmhing arid settling, lost the
greater part uf its c~rigiiinl dust. The dew-point tletermined
~J Y Espy, a t the I)eginning of any experiment, corrrspt~nded
to the first stage of cooling and the formation I J ~ fog on dust
nuclei ; lJL1t the dew-poiut cleterminetl hy him a few days
later in the same air when i t had become dustless IJY settling
He snyy :
374
W 2"
MONTHLY WEATHER REVIEW.
................. 1 ................ 69.4
OCTOBER, 1896
7,112.0 6.069.7 '5.876.7
6 201 9
~ ~ ~ ~~ ~ ~ ~~
represented the second stage when the vapor particles must
coudei~se on themselves only, which process required a
greater cooliug and a greater expansion.
Tacubays (0ls.Nac.) ........... I oluca.. ........................ Twjo (Hac.SlIao,Gto.) ................ Zauateuas ..................... Zapotlan (Semlnarlo) ...........
I.
MEXICAN CLIMBTOLOGICAL DATA.
I n order to extend the isobars and isotherms southward so
that the students of weather, climate and storms in the United
States may properly appreciate the influence of the condi tioiis
that prevail over Mexico the Editor has trauslated the follow-
ing tables from the current niimbers of the Boletin Mensual
as published by the Central Meteorological Oljservatory of
Mexico. The data there given in metric ineasnres have beeii
converted into English measures. The barometric Ineans are
as given by iiiercurial tmrometers uiicler the influence of lucal
gravity, and therefore need reductions to standarcl gravity,
drpending upon both latitude ant1 altitude ; the influence of'
the latter is rather nilcertain, Init that of the foriiir~ is well
known. For the sake of coiiforniity with the other data
piiJ)lished in this REVIEW these corrections for local gravity
have not been applied.
Me.&xm datu fm A ~/g i i ~f , 1596.
7, ti20.2 8,612.4
8,015.2 5,124.8
ai 'EI
c Stations. ." 5 -
I Colima (Seminarlo) ............. coiima.. ......................... Guadalajara (0bs.d. Est.). ...... ouaoajuato Jalapa.. Lagos (Liceo Querra) ........... Leon. ........................... 1 Magdalena (Sonora) ............ I
lVazatlau ........................ Merlda hlexico (Obs. Cent.).. Mexico tE.N.de S.) Morelia (Seminario) ............. oaxaca .......................... Pabellon ........................ Prcbuco ........................ Puebla (Col. Cat.) .............. Q ueretaro ....................... Snltillo (Col. S.Juan) ...........
..................... ......................... I
......................... ........... .............
sall r.uis PotoJi .................
m .
2 8 w 2
E - __
hCh. 28.30
25. a3 23.74
25.111
24.20
24.35
29.91
29. Y7
23.12
23.11
24.01
25.11
Z'. 5Y 23.43
24.23
......
.....
......
.... .... e. ne.
69.1 58 2.49 ne. ne. 70.0 1 a 1.81 1 se. e.,ene. E!!. 6 19.57 1 s.
..........
................. .......... 57.9 67:;i cti tIL1.; 0 .z 1 ne.
........ l e ,
...... ' ............ 3.m .......... B 67" 65 7 80 159 e 25:11 I I...... ! 7:14 1 n: 1
e.
e.
e.
ne.
n.t?
UNRELIABLE POPULAR WEATHER PROVERBS.
Many persons still fail to realize the fact that the weather
proverbs which pass down from generation to generation as
ui~qurstioned as are the nursery stories, teloug to what may
Iw prolwrly called mythology. Like the myths and legends
IJf ancient times they may, possibly, have had some slight.
Imsis of fact ; they may possibly have applied sat isfnctorily
tu some far oft' period and some far dietant land, or to oiw
spwial occasion, ]Jilt do not, necesfiarily, hold good to-day
:ind in oiir own couiitry. A t a recent rneetingof the Rfeteoro-
logical Society of France the members discussed the popular
proverb : " When i t rains on St. hledard's day it will rail1 for
forty days unless fine weather returns 011 the day of St. Der-
iial)e." M. Teisserenc de Bort sliowed that M. Lancmter,
\vho, several years ago examined this question, found no re-
sults tending to verify this saying. hf. Teisserenc de Bort
ltas also studied the question as to whether it was posqjble
t u predict ill advance a rainy period ; thus in examining $he
data collected froni 1863 to 1896, he finds that in the first
days (Jf JU~X the rain is, on the average, a little more abund-
:lilt, mid diminishes toward the end of that month. But i t
\vas not observed that there W ~B any systeniatic grouping of
the dtiys of rain around the day of St. Medard.
RI. Kenon said that M. E l k de Beaumont has called atteii-
tion to the fact that the proverh relative to Et. Medard dates
froni the middle ages, ancl that since theu the order of the
saiut's days in the calendar has heen changed, and that now
the day of St. Qervais is the one to which the proverh should
be applied. M. de Beauniont, therefore, examined the ques-
tion of the grouping of days of rain according to the new
date but did not fiiicl any verificatiun of the proverb.
THE EFFECT OF SHADING THE SOIL.
According to Lancaster (C'ial et Terre, Rlarch, 1S96, SVTI,
p. 33), some experiments have been made I J ~ A. Bnehler,
which niay be summarized as follows : Pour broad plats of
ground were selected, situated near each other; one was left
freely exposed to the sun and wind while the three others
were shaded by horizontal W O O ~P U trellises placed around
rnch piat niid afmtit 40 centirnetrrs aboi-e the ground. The
snuliglit ivits cut uft' fr(Jl11 the grou~ic1 by the shadow of the
trellis to a different estrnt for each plat, viz, one-quarter for
plat No. 3, one-half for No. 3, ancl three-quarters for No. 4.
In each plat, a t 5 centimeters below the soil, a thermometer
11 ay huried ; there was also placet1 in each plat an evnpo-
rorneter and a vase of sheet iron filled with clay in which
1,000 grains of water hod beeri poured. Observations were
taken every three hours, with the followiiig reoults: The
shaded soil esperienced less cooling hy radiation a t night-
time and less warining hy sunshine in the daytime. The
plat, No. 4, thrpe-fourths of whose area was shaded, showed a
trniperature 10 per cent lower than the unshaded plat, NU.
1 ; the lowering of temperature was most decided a t noon
and 3 11. ni. As tv the nocturn:~I cooling, the differriices be-
twwn the various plats were only 2 O C'. a t the niaxiniui~i,
wliich esplains why plaiits under a trellis are less exposed to
frost than plants that are not thus protected. During rainy
weather the differrnces i n temperntiire were very anit111,
rarely niore than lo C.; the slindecl plats had a temperatiire
a little higher than the unsliadrd, but during dry weather
the sliaded plats were warmed u p inore slowly. The relative
rvapration from the plats was as follows : No. 1, unpro-
tected, 100 per cent; No. 2, onequarter covered, SS per cent;
No. 3, ont.-half covered, 71 per cent; No. 4, three-quarters
covered, 68 per cent. Evaporation was most rapid from
uoon to 3 p. 111. The observations all rfhlate to n soil that is
not covered with vegetation. If the soil had 1)et.n cultivated
the temperature and the evaporation would have been di-
minished still more.
A PRIZE FOR KITE FLYERS.
Owing to his great interest in everytlriiig Learing on aero-
nautics, Mr. Octave Chanute, of Cllicagci, recently authorized
the Bostim Aeroiiau tical seciety t(J iiivite coinpetition for a
spacial prize for the liest moiicigraph u n the kite, giving a f u l l
theory of its nieclianics and stallility, w i t h cluaiititative coin-
pntntioiis appended ; the prize to he nwnrdcd I)y judges ap-
pointed by the fiociety. 'It was originally iiiteiided that the
conipetition for this prize ShCJ11ld close 011 Noveniber 15, 1896,
hut by a recent circular of Novenilwr 33 )\e lrarii that tlir
date has her11 I)(~stpoIletl to J i ~~i t ~i ~r y 1, 1SR7. I)c)ul,tless ~n t ~n y
of our readers will liavr intertAstetl tliemsrlvrs in kitr flying
for sciw~tiflc ~~I ~~N J W S sufficieiitly to have, :it leapt, tlionght
of competing f o r this prizr. The kite proniises to beCo11W a
very impurtaiit factor i n tlie t.splor;itiuii of the stniosphere
and we shall a l l look forward with interest to the publication
of that prize essay.
Ahout, 1PsO the Editor fuund a lad iu n'asliington who
hac1 kept his k i t r in the air continuously for the greater part
of two days and could have kept it there for a week louger.
up to that timc the Editor liad used and thought of the kite
only 8s a iiieiius of getting occasional records of tlie coiidi-
tion uf the upper currents, but ever since that date he has