12 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



know mast exist in the upper strata of our atmosphere there 

 can be iron vapor. Is it possible that iron possesses the prop- 

 erty of occluding the gas whose distinctive line is K 1474? If 

 it be so, this gas must be under ordinary circumstances of 

 temperature and pressure almost immeasurably rare." 



ox THE TEMPERATUEE OF THE SOLAK SPOTS. 



In presenting to the Paris Academy of Sciences the results 

 of some of his observations upon the temperature of the sun, 

 Mr. Langley, of Pittsburg, says that he has endeavored to 

 repeat the observations made by Professor Joseph Henry in 

 1845, and Father Secchi in 1852. He has employed an ordi- 

 nary achromatic refractor, after having first experimented 

 with and laid aside a fixed horizontal telescope whose lenses 

 were of rock-salt. The differences of temperature have been 

 measured by an extremely delicate thermopile made of ex- 

 tremely small bars of bismuth and antimony, the exposed 

 face of which has a diameter less than the sixth part of an 

 inch, within which area are seen the ends of sixteen pairs of 

 bars. This thermopile is connected with a Thomson's reflect- 

 ing galvanometer. This combination possesses such an ex- 

 treme sensibility that the galvanometer is, in spite of ordinary 

 precautions, continually registering foreign radiations, such 

 as would render indistinct the delicate phenomena that are 

 the subject of the investigation. These disturbances are 

 best removed by inclosing the pile within a blackened cylin- 

 der filled w^ith water at a constant temperature. The image 

 of the sun being about twenty-four inches in diameter, the 

 thermopile can be placed at any part thereof with great ac- 

 curacy. A second similar thermopile being placed in any 

 other portion of the solar image, and connected with the 

 same galvanometer, Mr. Langley was, by this differential ar- 

 rangement, enabled to make the desired measurements. His 

 observations confirm fully the original observations of Pro- 

 fessor Henry, and have led him to further interesting results. 

 From the known efiect of the diminution of the light of the 

 sun toward its borders, it seemed natural to conclude that a 

 proportional diminution of the heat of the sun would be ex- 

 perienced. Mr. Langley, however, finds that the heat does 

 not become insensible after we pass away from the visible 

 border of the sun, but continues sensible at a distance of at 



