Samuel Pierjpont Langley. 321 



Professor SAMUEL PIERPONT LANGLEY. 



In the death of the Secretary of the Smithsonian Institution, 

 America loses its most prominent astronomer and physicist. 

 Professor Langley was born in Roxbury, near Boston, August 

 22,1834, and died February 27, 1906. In this interval of 

 over seventy-one years he contributed immensely to the study 

 of the physics of the solar atmosphere and of the earth's atmos- 

 phere, besides also taking a prominent part in practical work, 

 such as the distribution of standard time, and development of the 

 aeroplane, considered as a flying machine. His popular writings 

 are distinguished by a beautiful diction, and the pleasure 

 that he took in conversing with young students is proverbial. 



After studying at the Boston High School, making a special 

 preparation as architect and civil engineer, and filling tempor- 

 ary positions in the Observatory of Harvard College and the 

 U. S. Naval Academy, he settled, in 1867, as director of the 

 Allegheny Observatory ; at the same time the present writer 

 settled at Cincinnati Observatory, and from that to the present 

 the close relationship of the subjects in which we were inter- 

 ested has produced a corresponding personal intimacy. Especi- 

 ally were we for many years first united in the effort to intro- 

 duce a uniform system of time signals that should be controlled 

 by local observatories, and be a means of support for these 

 institutions in their straightened finances. 



While devoting much thought to practical astronomy during 

 1867-1875, Professor Langley still found time to devote his 

 equatorial to the study of the sun's surface and his drawings of the 

 details of the spots have all the wonderful characteristics of the 

 rarest and best of modern photographs. His attempts to meas- 

 ure the relative temperatures of the spot and the surface, by the 

 thermo-electric method, led to his development of that form of 

 the electric resistance thermometer, which he called the " bolo- 

 meter." Each form of thermometer has its special troubles, 

 and the bolometer is no exception. For twenty years we have 

 been accustomed to receive pamphlets and memoirs, detailing 

 the steady progress made by himself or his assistants in 

 improving the sensitiveness and accuracy of the bolometer. 

 Notwithstanding the rival apparatus of Angstrom and the ther- 

 mopile, the bolometer is still in favor; of course both instru- 

 ments must be used side by side if we would attain results 

 better than either one can give alone. 



By applying the bolometer to the solar spectrum Langley 

 was able to reach far beyond the limit before recognized and to 

 measure the relative distribution of heat throughout the whole 

 extent of the spectrum ; he thus laid the foundation for all 

 modern study of the special absorbing and radiating powers of 

 atmospheres and gases for the individual wave lengths of light. 



