THE WHITER PITTSBURGH 



447 



time has been supplied from various observatories to nearly all rail- 

 roads. Returning after a number of solar eclipse expeditions, Langley 

 began, about 1870 to study solar phenomena, in which he became one 

 of the highest authorities, proving, among other things, that the absorp- 

 tion by the earth's atmosphere of solar heat is variable, and that sun- 

 spots have no appreciable effect upon the temperature of the earth. 

 In 1885 he gave the results of some of his investigations in solar phe- 

 nomena before the Royal Society in London. During his charge of 

 the Allegheny Observatory he contributed upwards of a hundred papers 

 to scientific journals. In his studies of solar physics, recognizing that 

 the instruments were inadequate to record much of the sun's radiant 



Kntrance to Highland Park. 



energy, he began a long series of experiments which resulted in the 

 invention of that marvelously delicate instrument, the bolometer. With 

 this perfected, he renewed his investigations of the sun, moon and stars, 

 which brought to light facts as important as any in the whole realm of 

 astronomical physics. 



Beginning with Langley's charge of the observatory there had 

 grown up a valuable and intimate association with John A. Brashear, 

 which continued after Langley's transference to the Smithsonian Insti- 

 tution, and until his death. The bolometer could not have achieved its 

 wonderful success without Brashear's mechanical and scientific assist- 

 ance. Experiments had shown that transparent crystals of rock-salt 

 have the faculty of transmitting the low heat rays of the sun (that is, 



