452 MONTHLY WEATHER REVIEW. SEPTEMBER, 1917
8OME NUCLEI OF CLOUDY CONDENSATION.
By Dr. J. AITKEN.
(Presented to the Royal Society, Mar. 19, 1917.)
[A&lmetrcprinttdfrom Nature, London, May 17,1917,99138.1
By means of an improved apparatus for producing a
series of defjnite espansions of a given volume of saturated air, the author studied the cloud-producing qualities of
dust partides of different sizes obtained in various ways. After the air was cleared of the largest particles by one or more applications of a 2 per cent espansion, cloucl- producing particles o smaller sizes were removed in suo-
cession by espansions 4 per cent., 6 per cent, 8 per cent. and so on up to 20 per cent,, if necessary. The particles were produced by such means as flames, electric spark? chemical act.ion, and heating of solid substances; and the general conclusion was that in no espansion lower than
25 per cent was there any evidence of elect.ric. ions being by thenwelves efficient nuclei for cloudy condensation. The view that the nuclei of cloudy condensation pro- duced by heat are ions dischar ed at high temperatures
lower temperatures than that at which ionic discharge from heated bodies occurs; and even a t this hi her tem-
chemical or disintegrating action takes place along with the discharge of the ions.
is not supported, since such nuc 5 ei are produced at much
perature spectroscopic esainination shows t k iat some
CONDENSATION AND EVAPOBATION OF GAS MOLECULES.
By I. LANGYUIR.
[Reprinlcdfrorfl Scienre Abstracts, Sect. A, July 30, 1917. $851.1
Previous work by the nuthor gave evidence that atoiiis of tungsten, molybdenum, or platinum vapors: striking R
clean, dry glass surface in high vacuum, are coudensed as solids at the first collision wit,h the surface. Sindar evidence was obtained froni a study of chemical reactions in gases at low pressures. It was concluded that in general, when gas inolecules strike a surface, the ma ority
collisions, but a.re held by cohesive forces until they evaporate from the surface. In this way a theory of adsorption was developed which has been thoroughly confbmed by 'later esperiments, viz, the amount of
material adsorbed depends on a kinetic e uilibrium
tion from. the surface. Practicalll every molecule striking the surface condenses (in ependently of the temperature), while the rate of evaporation depends on
the teniperature and is proportional to the fraction of the surface covered by the adsorbed material. R. W. Wood's experiments on mercury atoms impinging on a lass plate tit definite temperatures are referred to and
%sewed, following which comes a review of Wood's experiments on a stream of cadniiuin atom, which streani on striking walls of a well-exhausted glass bulb does not form a visible deposit unless the glass is at a temperature below about- 90C., but when started the deposit con-
tinues to grow in thickness even after i t is warmed to room temperature. Wood concludes that nearly all atoms of cadmium are reflected from surfaces other than cadmium if the initial temperature is above -9OOC.
The present author criticizes this reflection theory and proposes as a better alternative the condensation-
of them do not rebound from the surface by e f astic
between the rate of condensation and the rat,e o 7 evapora-
I Proreed., Nat'l Acad. Sri.. March. 1917. 3:141-147.
eva oration theory, and, to determine definitely which
repeated Wood's experiments under modified conditions which are described at some length. The experiments prove that single cadmium atoms actually evaporate off of a glass surface at temperatures below room temperature, although they do nol; do so at an appreciable rate from a cadmiumsuilace. The condensation-evaporation theory thus verified affords very satisfact,oq esplanation of Moser's breath-fi ures on glass and the Jeculiar effect
panes. The author o ines his t.heory to be capTble of
includin the ri.?-~t,nllixat.ion c-jf subcoolad liquids.--
of t g e two theories correspond best with the facts, he has
observed in the P onuation of frost, oryst. &!l s on window-
estension to the who T P subject of nucleus formations,
H. H. &[dgsOn.]
COMPUTATION AND MEASUBEMENT OF THE COMPLEX
MOLECULES OF SOME VAPORS, ACCORDING TO THE
NEW CONDENSATION THEORY.'
I3y I,. .hmfix.
[Krpr.inledfrorrr Science Abslrwts. Ssrt. A. AUK. 3U, 1917, $ is:.]
4: * * f l
llie series of esperiinents were conducted in t.he abseiice of any elec.tric field; with electric field up to 3.70 volt.s/cni ; by incrensing the never-absent radio-
uct.ive radiatioiis of the atmosphere and earth with the a.id of pitchblentlc and of weak and stroii radium prep- arations, first wit.11 wa.t,er vapor and air. &e experimenh with CO, as gas ave much the same resu1t.s. When the gas was liyclrogen t 5 e results differed froiii those previously obtained when the mall [spherical ex ansion chamber) was used, but a reed auain when the P arge sphere [260
1x1. cm.] was apaied: #iW+condeiisation chamber, it is poiiited out, was still siiider than t,he author's siiiall
[60 ou. c.iii.1 sphere. Nc.ohol was tried inked with air and with hydrogen; benzene only in air mixtures. The gen- eral conclusion drawn is that the ordinary condensation by expunsion depends mainly on the formation of elec- txicallg neutral coniples vapor molecules and their size and suifac.e t.ension. and is hencc independent of the gas containing the va 101'8, while the elect,ric carriers (ions)
tric nuclei is a function of tlie vapor: the presence of
traces of foreign vapois has no influence, provided chemn- ical reactions (due to radiations) be escluded; the nuclei consist hence of coniples polyinerized vapor molecules. In addition to t,hese nonelectric nuclei there are electric carriers of both polarities, clue t,o the radiations (terres- txial and atmospheric) ; they make up perhaps 1 per cent of the whole nuclei and consist predominantly also of vapor niolecules. In size the nuclei differ with the nature of the liquid (vapor) ; but there is no discontinuity be- tween the mists and the drops of a vapor, and the two types of condensation can not be differentiated by defi- nite espansion values. The electric cnrriers are always the largest nuclei; their nuniber naturally depends also
on the gas; their number, 900 (no esternal field), would correspond to the 0.4 carriers per second per cu.
(:.in. assumed to account for the very small residual con-
saturation degree is 5 or more, some ve
ical reactions caused by the terrestrial radiations (H,Oz, Os, etc.). By far the reater number of nonelectnc nuclei are, however, smalfin size and consist. of complexes of only a few (2 or 3) niolecules; their number, deter-
play on1y.a secon d ary part.. Tho forina.tion of nonelec-
ductivity of t,he air. There are,
tric nuclei (0.1 per cent of total number)
. . . . . . - - ._ - .
I Ana. d. Fhysik, Feh. 4.19li. 521:l-il.
SEPTEMBER, 1917. MONTHLY WEATHER REVIEW. 468
mined for each va or at ordinary temperature, is: water
cent of the total vapor molecules present, which would correspond to about 100,000,340,000,190,000 molecules er cu. cm. These nonelectric molecules are characteristic for each vapor. Exposure of the va or-gas iiiixtures t.0
and thus the nuniberr) of molecules per nucleus, to 8 for water and 6 for alcohol; and increases also in particular their number very niuch, in accordance with the radiation intensity. Lenards theory supplemenbs Kelvins theory b adding a term depending on the ratio of the portion
and on the surface tension which varies with the radius and the thickness of t,he liquid shell. It also diffeis from J. J. Thonisons theory in so far as with increasing es- pansion a supersaturation is said to be reached at ivhich all the nuclei are condensed; the total number of nuclei in water vapor (no esternal field) seems to be limited to lo5, as stated.--H. B[~omts].
1.9X lo-, ethyl Bf coho1 2.5 X lo-, benzene 0.8 X lo- per
0 and y rahations, further increases t i e size of the nuclei,
o 9 the drop surface from which evaporation can t,ake place,
GT/. 57-3 ( 0 Y B ) A NEW EVAPOBATION FOBMULA.
By R. E. HORTON.
[Rrprinlrd from Science Abstracts, Sect. A. 4ug. 30,1917,# i91.1
in180Dalton deduced the foiiiiulaE =C(V-v), where E is the rate of evaporation froni a liquid surface, V the vapor pressure corresponding with. the temperature of the liquid, 27 the vapor pressure existing in the atmosphere at the time and C is a constant. The effect of the wind was allowed for by var ing the value of C. Later workeis
d o w for the wind speed LV. According to the forniula thus modified, the rate of evaporation increases indefi- nitely with increase of wind, whereas in practice a masi- inum value is obtained when the wind velocity reaches 15
to 30 miles an hour, and above this there is no further increase. The author, therefore, prefers to allow for wind by the introduction of an exponential factor, and de- duces t8he equation,
E=C[(2-e-k-kw)V-Z].
Values of the coefficient (2- ck)rnay be read off from a graph thus simplif ing the working. The formula is
hunlidity condensation will take place in st,ill air, while there will be slight evaporation under the same condi- tions in a wind. This result has been verified in prac- tice. The formula as stated applies to a small liquid surface. The latt,er part of the paper is devoted to a consideration of the case of a larger area where the evapo- ration from the leeward part will be hindered by the presence of the vapor given off by theapart niore to wind- ward. The author states that it will, in many cases, be more accurate to calculate the rate of evaporation froni a large water surface by means of the formulaz here put forward, than to rely on attempts a t direct measurement with the ordinary type of evaporinieter.-J. S. Di[nae].
have usually intro d uced a factor of the form (1 +kw) to
also a plicable to t i e case of condensation. It will be seen t P iat under certain coliclibions of t.emperature and
6-3-/.*5-y8. / : 6 3 4
FORESTS-AND-FALL EXPEBIllbENTS. .
There appeared in Nature, for ,4u st 2, 1917 (pp. 445446), a review by Mr. Hugh R. Ell, of the recent
1 Engineering NBWS-ReCmd, New York, Apr. 26,1917, 7&196-199.
Indian Forest Bulletin No. 33 by M. Hill, chid c o d sioner of forests of the Central Provinces. Dr. Gilbert Walker of the Indian Meteorological Department con- tributed two appendices to that bulletin, and concerning
nr. Walkers conclusions lfr. Mill says in part:
J?r. Walker considera that, aa Blanford pointed out in 1887, the on1 mtisfactory evidence would be that obtained by comparing the rainhi of a district when well supplied with forests with that of the =me district when the trees were very few. In our opinion the comparkn should not be that of a district A at the time t with the same district at the time t; but to conipare the relation of district A to a contiguous district B at the time t with the relation of A to B at time t/. where A is a district that has undergone a great change 89 regards forest covering, while B haa remained unchanged. The reaeon for this indirect com- parison is. of course. to eliminate the effect of the two periods Mli in
what Prof. H. II. Turner calls different climatic chaptera. An%er method would be to deterniine the relation of the isohyetal lines to the conflguration of the land on wooded and treeless districts of mmileu character. As pointed out in the report on the rainf?ll in the Geolo cal Survefs . Water Supply Memoire of Hamphire, the district oathe Xew h e s t shows a considerably higher general rainfall than ita elevation above sealevel ap ears to suggest. The subject is bqth fascinating and important, ani the time will no doubt come when in- crease of accurate observations will enable the vague belief in the beneficial influence of forests on climate to be supported or corrected by detinite ineteorologicnl evidence.
It seems appropriate here to recall the circumstunce that precisely the first method here suggested by Mr. . Mill for adving the problem of the relations between rain- fall anfforestatiori was adopted by the United States Weather Bureau in 1910, cooperating with the United Stn tes Forest Service. These two services have selected two contiguous and practically inden tical watersheds in the Rio Grande National Forest (lat. 37 45 N., long.
1 0 6 O 50 W., alt. 9,400-11,000 feet) near wagon Wheel Gap stittioil on the Denver & Rio Grande Railroad, at present under identical forested conditions, and have established therein a large number of thermometer, precipitation, and streani-gage stations. Careful obser- vations will be carried on in both watersheds for a number of Sears and a t the conclusion of t-his first period one
of the watersheds will he deforested and the same obser- vat ions continued for n second period corresponding to
the first one. Already we hare secured nearly a full 6-years record there, as observations actually began October 32, 1910. While the United States seems to have been the first to take this step, it is certainlydesirable that as many other countries as possible should make the same test. Mr. Mill, it is not likely that a m . area in UniteB States is sufficiently supplied with well-dist ributed raingages to encoura e one in undertaking the computational labor involvef-c. A., jr.
Concerning t8he second method sumvested b
EXCESSIVE PXECIPITATION IN LONDON, ENGLAND.
[Repintdfrom Nature, London, June 21,1917.99328J
Dr. H. R. Mill records, in the London Times of June 19, 1917, that the thunderstorm between 5 and 7 p. m. (summer time) a on Saturday, June 16, was, if measured by rainfall, one of the most severe ever experienced.in London. More than 2 inches fell over an area measuring 10 miles from Barnes to Finsbury Park and 4 miles from Hyde Park to Willesden Green. A t two oints within this area more than 3 inches was reportex-viz,
riment is described in detail in the MONTELY W E A ~E REVIEW, &p-
t S 2 %18:1453-1455. with map.
3 s18&m& Time.* This is the first reference in the MONTBLY W Z A T ~E REVIEW to the Ida light 1 use among Europesn countries ante 1916. Summer time in England is I s f a s t e r than QreenWich Mean Time. A presentation of the advantages and dlsadvantagas of 8ummer Time. as develo ed bv a year of actual es erience therewith, wU he found in Review 01 Reviews,%ew kork, June, 1916, pp. h5-716.-C. A., Jr.
scheme that has been in such