Proceedings 243 



A communication from the Carnegie Institute of Chicago 

 was read and referred to the Astronomical section with power 

 to act. 



260th Meeting, May 20, 1902. 



Chemistry Lecture room, University of Minnesota. 



President Hall in the chair. 



A good audience present. 



J. P. Magnusson of Brainerd, S. J. Race of Redwood Falls, 

 C. W. Sage, of Fountain, and C. W. Jackson, of Hallock, were 

 elected members. 



Professor H. T. Eddy gave a lecture on Attenuation and 

 Distortion of Long-Distance Telephone and Power Transmis- 

 sion Lines regarded as Hydrodynamic Phenomena. 



[abstract.] 



The analogy of a steady flow of water in a long pipe under the 

 action of a constant head and a continuous current of electricity under 

 a constant pressure such as is furnished by one or more cells of a bat- 

 tery, has often been employed to give a clear elementary physical con- 

 ception of the mathematical relations expressed by Ohm's law. In this 

 case the applied pressure is gradually consumed by the resistance ex- 

 perienced by the current, and in strict analogy with the flow of water, 

 the loss per unit of length is proportional to the product of the square 

 of the current and the first power of the resistance. So far as the 

 mathematical relations are concerned the two problems are identical. 



The object of this paper was to extend this hydrodynamic analogy 

 to the more complicated case of long distance transmission of alternat- 

 ing currents in general. 



Telephone transmission was specifically mentioned in the title in 

 order to include the general case of variable frequency. The import- 

 ance of thus extending and enlarging this analogy is evident when we 

 reflect that all the complicated phenomena of long distance lines and 

 cables with their sending and receiving apparatus may be completely 

 reproduced in all its details of operation by simple pumping machinery 

 with its transmission pipes and air chambers, whose manner of oper- 

 ation may be made clear to any one without the aid of higher analysis. 



In conclusion, it may readily be shown that in both of the two 

 extreme cases already considered, viz., those in which either friction 

 or inertia is disregarded, the logarithm of the reciprocal of the 

 amplitude, or intensity of wave at any point, varies directly as the 

 product of the distance of the point from the source of the wave by 

 its velocity. Since this velocity has already been shown to be con- 

 stant in case the fluid friction may be disregarded and to increase with 

 the frequency in case the inertia be disregarded, it is evident that the 



