1880.] 



President's Address. 



89 



Captain Abney has opened out to us a new region beyond the red. 

 Lord Rayleigh and others before him have, however, proved that 

 there must be a limit at the least refrangible end of the spectrum. 

 Professor Stokes, long since, noticed the difference in length between 

 the spectrum of the sun and that of the electric arc ; and M. Cornu 

 has recently shown by observations at elevated stations that the great 

 rapidity of atmospheric absorption must preclude the hope of any 

 great extension of the solar spectrum toward the more refrangible 

 end. 



The striking advances made in electricity during the last few years, 

 and marked by, among other things, the inventions of the telephone 

 and the microphone, have been followed- by a step not less daring in 

 its conception, nor less successful in its execution ; I allude, of course, 

 to the photophone, the result of the researches of Mr. Graham Bell 

 and Mr. Sumner Tainter. The principle of this instrument is already 

 known. A powerful beam of light is first thrown upon a flexible 

 mirror, the curvature of which is modified through vibrations set up 

 in it by the human voice. The reflected beam is then received by 

 a selenium " cell," forming part of an electric circuit. The in- 

 tensity of the light so received, and with it the resistance in the 

 circuit due to the selenium, varies with the varying curvature of the 

 flexible mirror. A large parabolic mirror is used at the distant station 

 to concentrate the light on the selenium " cell;'* and a telephone in 

 the circuit reproduces the variations in the form of sound. 



Mr. Bell has, however, also shown that rays from the sun, or an 

 electric lamp, when rendered intermittent by any convenient means, 

 will set up in a plate of almost any substance vibrations corresponding 

 to the intermittence. The substances as yet tried are : metals of 

 various kinds, wood, india-rubber, ebonite, and many others, and 

 among them zinc appears to be one of the best suited for the purpose. 

 This result, which is independent of any electric action, is, perhaps, 

 due to heat rather than to light. 



In these, as in many other issues of scientific research, we can 

 hardly fail to be impressed by the almost inexhaustible resources 

 which lie ready to hand, if we only knew how to use them, for the 

 interpretation of nature, or for the practical purposes of mankind. 



During the past year Professor Hughes employed his induction 

 balance for the detection of very minute impurities in small masses 

 of gold. Mr. Preece also has shown how slight increments of 

 temperature in fine wires transmitting telephonic currents of 

 electricity, will sufiice to reproduce sonorous vibrations ; and even 

 articulate speech at a distant station by their influence on thin 

 platinum wires, only six inches in length. 



Mr. Stroh has shown that, at the point of contact of two metals 

 carrying strong electric currents, adhesion takes place, varying with 



