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. Lenard’s theory supplemenbs Kelvin’s 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. Thonison’s 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
in180’Dalton 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. Walker’s 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