METEOROLOGY. 413 



From this it will be seen that the resistance is least for water, some- 

 what greater for smooth sand, and greater still for grass. Further ob- 

 servations are not only required on this subject, but also on the velocity 

 of the wind over the water in relation to the height of the waves. {Na- 

 ture, XXV, p. GOT.) 



Some experiments have lately been made by the Eev. Dr. Haughton 

 and Prof. Emerson Eeynolds to evaluate the coefidcient of friction (i e., 

 the "drag") of air upon air and of water upon water. In these ex- 

 periments a spherical ball of unpolished granite of 22 kilograms weight 

 and 25 centimeters in diameter was suspended freely by a pianoforte 

 wire, and was set rotating in the air or in water, the period of the vi- 

 brations and the decrement of their amplitudes being observed by 

 means of indices attached to the brass collar by which the ball was 

 suspended. A discussion of the equations of motion led to a simple 

 working equation for the reduction of results. The mean coefficient of 

 friction found for air upon air was/= 6F52T) though this value appar- 

 ently differed slightly according to barometric and thermometric con- 

 ditions. For the " drag " of water upon water the value found was 

 /= 3^iy. These experiments involved friction at low velocities only, 

 for which it could be assumed that the friction was proportional to the 

 velocity. The authors of this research point out that these results 

 tend to negative the theory of Dr. Carpenter that the phenomena of 

 ocean circulation are due to the greater height of the water at the 

 equator as compared with that at the poles. (Nature, xxii, p. 207.) 



P. Volkmann has made a new determination of the specific gravity of 

 pure mercury, in which he makes allowance for a new source of error 

 depending on the change of volume of the vessel due to the internal 

 pressure of the heavy liquid. Assuming the density of water at 0° 

 centigrade to be 0.999881, he finds the density of mercury at 0° to be 

 13.5953 ± 0.0001, which is a little less than the lowest of the values 

 given by Regnault, whose average result, 13.596, is the value ordinarily 

 adopted. 



V. — a Solar radiation; h Terrestrial temperature. 



C. W. Siemens has advanced a thoroughly original theory of the con- 

 servation of solar energy in a paper read at the Koyal Society, March 

 2, 1882. He supposes stellar space to be filled with highly rarefied gas- 

 eous bodies besides solid material in the form of dust. Each planetary 

 body and the sun attracts to itself an atmosphere, and the solar system 

 as a whole contains an interplanetary atmosphere, denser than the 

 extremely rarefied stellar space. He considers that aqueous vapor and 

 carbon compounds are present in stellar or interplanetary space ; that 

 these gaseous compounds are capable of being dissociated by radiant 

 solar energy while in a state of extreme attenuation ; again, that these 

 dissociated vapors are capable of being compressed into the solar pho- 

 tosphere by a process of interchange with an equal amount of reasso- 



