460 



SCIENCE. 



[N.S. Vol. XVI. No. 403. 



the magnitude of those received by it. Any 

 discontinuity of mass in the current flowing 

 in the pipe, as for example, mercury in 

 place of water for some part of the length 

 of the pipe, will originate reflected or re- 

 turn waves. To insure good transmission, 

 little or no discontinuity in the distribution 

 of the inertia along the pipe should occur 

 at any point such as would be due to 

 changes of size or otherwise. 



All these results are equally true of al- 

 ternating-current circuits. 



It may be shown from elementary con- 

 siderations that the progressive velocity of 

 the waves in the transmission pipe under 

 consideration is constant for all frequencies 

 of oscillation in case of a pipe in which the 

 friction may be disregarded, but that the 

 velocity increases as the square root of the 

 frequency in any case where the inertia of 

 the current may be disregarded. The case 

 of the unequal velocity of the waves propa- 

 gating the harmonic components of sounds 

 in telephonic transmission by reason of their 

 diflierence of pitch, which is one cause of the 

 distortion of sound in long-distance tele- 

 phone transmission, has been treated at 

 length in the researches of Dr. Pupin who 

 has investigated very fully the inductive 

 (or inertia) loading necessary to render 

 lines practically distortionless. This is 

 equally a hydrodynamic phenomenon. 



The one question remaining for elucida- 

 tion is that of the attenuation or gradual 

 diminution of amplitude of waves as they 

 progress along the line. 



It may be readily shown that in both of 

 the two extreme cases already considered, 

 viz., those in which either friction or iner- 

 tia is disregarded, that the logarithm of 

 the reciprocal of the amplitude, or intensity 

 of the 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 constant in case the fluid friction may 



be disregarded and to increase with the fre- 

 quency in case the inertia is disregarded, 

 it is evident that attenuation depends upon 

 frequency in case of fluid friction without 

 inertia, but it is independent of frequency 

 in case of inertia withoiit fluid friction. 

 Such unequal attenuation in the telephone 

 obliterates to a greater or less extent tones 

 of high pitch before it does those of lower 

 pitch. It is therefore necessary to distinct 

 transmission that the self induction of the 

 line should be large enough to store a large 

 amount of kinetic and potential energy in 

 the wave motion along the line, which in all 

 its aspects is strictly analogous to the wave 

 motion propagated in the water in the ap- 

 paratus just described. 



THE CABNEOIE INSTITUTION. 



The officers of the Carnegie Institution 

 have appointed advisory committees and 

 have invited suggestions from men of sci- 

 ence. The executive committee has there- 

 fore under consideration a large number of 

 reports and recommendations, but as these 

 must in large measure be regarded as confi- 

 dential, it is probable that the committee 

 would welcome a public discussion of the 

 entire question of the endowment of scien- 

 tific research. Science appears to be the 

 best place for such discussion ; and it would 

 doubtless be for the common good if those 

 who are interested in the subject would 

 make known their views before the meeting 

 of the trustees in November. At that time 

 a definite policy may be adopted, which can- 

 not thereafter be altered. There are so 

 many diverse possibilities and conflicting 

 interests that these can only be sifted and 

 reconciled by full and free discussion. 



It appears that the Carnegie Institu- 

 tion can either undertake certain large 

 plans for the promotion of science or. can 

 assist a great number of special researches, 



