Apkil 5, 1907] 



SCIENCE 



523 



tion of land and water, and by the insola- 

 tion, with its resultant temperature, evap- 

 oration and clouds. In the analytical 

 treatment of this problem, beginning with 

 d'Alembert, Ferrel and Erman, as well as 

 in the more elegant works of Helmholtz, 

 Oberbeck and Margules, it has always been 

 considered necessary to simplify the prob- 

 lem by assuming a uniform surface and 

 uniform coefficient of resistance for the 

 whole globe, as also a uniform condition 

 of dry air. In this shape the problem is 

 already very complicated, and it is likely 

 that the profound meteorological problem 

 of the deduction of the actual winds from 

 the laws of mechanics, will for a long time 

 be too difficult for pure analysis; but on 

 many occasions I have stated my belief 

 that a solution may be arrived at iu an 

 experimental way. 



We may represent any portion of the 

 globe, with its atmosphere, by a horizontal 

 plane surface, covered with some heavy gas 

 or liquid, such as a thin layer of carbonic- 

 acid gas, or alcohol, or water, which is to 

 be set in steady rotation, and may be 

 warmed from below in such a way as to 

 approximately imitate the actual isotherms 

 of the lower atmosphere. Special areas of 

 high and low temperature can easily be 

 imitated by electrical resistance coils. 

 These rotating areas are to be covered by 

 plates of glass, rotating with them. 



Various theorems relative to the simi- 

 larity of such a model to the atmosphere of 

 the earth were first published by Helmholtz 

 in 1873, 'On a Theorem Relative to Move- 

 ments that are Geometrically Similar in 

 Fluid Bodies, ' and these ideas were further 

 applied by him in memoirs on atmospheric 

 motions, in 1888 and 1889 ; and further de- 

 velopments have lately been given by Lord 

 Rayleigh. But in applying these ideas to 

 our two polar projections we stumble upon 

 a great difficulty, namely, that the maps are 



not true representations of the spherical 

 surface of the earth. 



In the present case we should like to pre- 

 serve the equality of surface areas; and to 

 preserve equality of distances, since we 

 have to compare velocities; and above all, 

 we should like to preserve the equality of 

 the moments of inertia. That which best 

 satisfies all desiderata seems to be Airy's 

 'projection by balance of errors,' published 

 by him in 1861. The combination of 

 Airy's development with Helmholtz 's 

 method of mechanical similarity should 

 enable us to interpret our laboratory ex- 

 periments. 



I consider it extremely desirable that 

 these experiments should be made on a 

 large scale, with due regard to all numer- 

 ical, statistical and mechanical details, in 

 some laboratory where the study of meteor- 

 ology is prosecuted as a branch of mathe- 

 matical physics. 



8ome New and Useful Data in Reference 



to the Moisture of the Air: Henet 



Emerson Wetherill, Philadelphia. 



This paper gave an outline of researches 



upon the relative humidity of the air, as 



determined with a new cobalt chloride 



scale and test paper, and referred to the 



use of a special instrument for measuring 



the moisture of the body in different 



diseases. 



References were made to new psychrom- 

 eters for correcting hygroscopes and to 

 studies of the measurement of the perspira- 

 tion, in malarial and other fevers, as 

 carried out in the Philippines, Panama and 

 elsewhere; and also to a cobalt hygroscope 

 depending upon the change of weight of 

 the test papers with humidity. The weigh- 

 ings of this change suggested the produc- 

 tion of an instrument that might be called 

 the hygrobaro, and one that would be of 

 service to the weather bureau. 



