516 PROCEEDINGS OF THE AMERICAN ACADEMY. 



of another year to incessant experiment for the purpose of devising a 

 more sensitive instrument than science then possessed. I cannot 

 remember that I took the principle from any source then familiar 

 to me ; but I think I was unconsciously guided by some dimly appre- 

 hended recollection of the electric pyrometer of Sir William Siemens, 

 which I certainly had read of before. 



When the bolometer was completed and in active work, I sought to 

 get a knowledge of the literature of the subject (if it had a literature), 

 and only then learned from my friend, Professor Rood, of the nearly 

 forgotten paper by Svanberg, and which I believe I was the means of 

 bringing to public notice in my first communication on the subject to 

 the Academy. 



At the request of the President, Professor Langley then 

 went on to speak informally to the Academy of some as yet 

 unpublished results of his work with the bolometer on the 

 heat-spectrum of the moon. 



The following papers were presented : — 



Biographical Notice of the late Ephraim Whitman Guruey. 

 By Charles F. Dunbar. 



The Law governing the Propagation of Signals in Electric 

 Circuits. By William W. Jacques. 



An Instrument for showing the forms of Undulatory Elec- 

 tric Currents. By William W. Jacques. 



On the Spectrum of the Sun. By John Trowbridge. 



The following papers were presented by title : — 



Contributions from the Physical Laboratory of Harvard 

 College : I. The Atmospheric Si:)ectrum, II. On the Ex- 

 istence of certain Elements in the Sun. HI. Radiation from 

 Rock-Surfaces. IV. Efficiency of Secondary Generators. By 

 John Trowbridge. 



Reduction Factor of a Galvanometer Coil. By J. J. 

 Skinner. 



