288 WRITINGS OF JOSEPH HENRY. [1849 



ology which it has undertaken to establish, has issued direc- 

 tions for the observation of the Aurora. These directions 

 are similar to a set issued by the directors of the observatory 

 at Toronto, for observers in Canada. The observations made 

 in the two countries will thus form one extended system. 

 The proprietors of the several telegraph lines have offered 

 to grant us the use of their wires for meteorological purposes, 

 and it is hoped when the lines are completed, and we have 

 established a set of observers, extending, for example, from 

 Toronto to Washington, or even farther south, we shall be 

 able to study the phenomenon of the Aurora with more pre- 

 cision than it has ever been studied. On a long line extend- 

 ing north and south, the observer, for example, at Toronto, 

 having noticed an Aurora, may call the attention to it of all 

 the observers along the line, and thus the.extent of the visi- 

 bility, and the simultaneous appearance of any peculiar 

 phase of the meteor, may be readily determined. 



ON THE DIFFUSION OF VAPOR.* 



(Proceedings American Association, Adv. of Science, vol. ii, pp. 127, 128.) 



August 16, 1849. 



Professor Henry remarked that he was much interested 

 in the experiment of Professor Horsford, in which vapor 

 was shown to pass through a tube filled with air. It is well 

 known that, according to the theory of Dalton, air and vapor 

 are vacuums to each other. This theory is certainly in accor- 

 dance with all the statical phenomena of the diffusion of 

 vapor, but does not as well represent the dynamic effects. 

 So great is the resistance to diffusion through a narrow tube, 

 that Professor Espy has concluded that the theory is incor- 

 rect, and that diffusion of vapor cannot take place without 

 the aid of a current of air. Professor Horsford's experiment 

 proves that a diffusion does take place through a tube, but 

 in this case the force of diffusion may be considered a max- 

 imum. 



♦[Remarks on a communication by Professor E. N. Horsford, to the 

 Association, "On the Moisture, Ammonia, and Organic Matter of the 

 Atmosphere."] 



