S28 SAMUEL PIERPOXT LAXGLEY. 



SAMUEL PIERPONT LAXGLEY (1S34-1906) 



Fellow in Class I, Section 2, 1883. 



What can a writer of a notice of Samuel Pierpont Langley, twelve 

 years after his death, add to the notices ah-eady published in the lead- 

 ing scientific societies of the world: especially the full notices at the 

 memorial meeting in the Smithsonian Institution, Dec. 3, 1906? 

 The American Academy of Arts and Sciences, however, would feel 

 that it would be lacking in respect to the memory of one of its most 

 distinguished members if it did not commemorate, even in a brief note, 

 his achievements. The American Academy early recognized his 

 al)ility by the bestowal of the Rumford medals; and it can now point 

 with pride to the justification of their confidence in the value of his 

 work. 



Samuel Pierpont Langley was born in Roxbury, ]Mass., Aug. 22, 

 1834. He was educated in the Boston Latin School and in the Boston 

 High School. HaA'ing adopted the profession of an architect and a 

 civil engineer, he went to the West and engaged for a time in practical 

 life; but his scientific tastes prevailed and he came back to the east 

 to take up the study of astronomy. He became an assistant in the 

 Harvard College Observatory, and at the age of thirty-two was ap- 

 pointed Director of the Allegheny Observatory, where he remained 

 for twenty years. 



He became a pioneer in the new subject of astrophysics and soon 

 began a series of investigations on radiant energy, especially mani- 

 fested in the solar spectrum. In his early experiments he used the 

 apparatus made classical by previous investigators — the combination 

 of junctions of bismuth and antimony, called the Melloni pile. These 

 junctions are very sensitive to radiant heat, and the thermo-electric 

 currents developed at the junctions can be measured by a suitable 

 instrument — a galvanometer — placed in an electric circuit — namely 

 the circuit of the junctions and the galvanometer. Langley found, as 

 so many did, that thermo-electricity cannot be depended upon for 

 accuracy of indications of ^ small amounts of heat. He therefore 

 adopted the electric balance, in which the increase of electrical resist- 

 ance in a coil submitted to heat, is balanced by other coils. The 

 electrical balance is what is known as the Wheatstone's Bridge. 

 Langley 's contribution to the electrical balance was the use of an 



