286 SCIENTIFIC RECORD FOR 1882. 



ally increasing from 1.25 to 11.4 tenth meters, corresponding to a motion 

 of recession increasing in two minutes from 36 to 330 miles a second. 

 Tiiirteen sun-spots have been examined on 20 daj'S with reference to 

 the broadening of the lines in their spectra. The strong black lines or 

 bands in the part of the spectrum between b and F, first noticed in the 

 spectrum of a spot on November 27, 1880, have been generally observed 

 to be present in the spectra of spots during the last twelve months, 

 besides several fine lines in the same region of the spectrum to which 

 there is nothing corresponding in the solar spectrum. 



For the determination of motions of stars in the line of sight, 177 

 measures have been made of the displacement of the F line in the 

 spectra of 41 stars, 68 of the &i line in 19 stars, and 9 of the 64 line in 

 5 stars. Of the 61 stars observed, 15 had not previously been ex- 

 amined', and the total number of stars of which the motions have been 

 spectroscopically determined is now 106. In the case of three of the 

 stars observed in the last year, a dispersive i)ower equivalent to that 

 given by sixteen prisms of 60° has been used. A comparison of the 

 successive determinations of the motion of Sirius indicates a progres- 

 sive diminution from about 22 miles a second, in 1877 and 1878, to about 

 7 miles a second or less this year, and as other stars do not show any- 

 thing similar, it appears likely that the change is due to the orbital 

 motion of Sirius. Further observations will, however, be required to 

 settle the point." 



THE SUN. 



Solar radiation. — Prof. S. P. Langley has submitted to the Chief Sig- 

 nal Officer an abstract of the results of the Mount Whitney Expedition 

 to determine the amount of heat the sun sends to the earth; in techni- 

 cal terms, the solar constant. Mount Whitney, in Southern California, 

 ■was selected for the observation because it combined the advantages of 

 great elevation, extreme dryness of atmosphere, and abrupt rise from 

 the plain. The party of observation consisted of Capt. O. E. Michaelis, 

 United States Armj' ; two non-commissioned officers of the Signal Serv- 

 ice, six soldiers acting as an escort, four civilian assistants, and Professor 

 Langley. Systematic work did not commence until the last days of Au- 

 gust, 1881. Professor Langley summarizes the results obtained as fol- 

 lows : 



''The approximate estimate of the solar constant is from 3.6 to 3.0 

 calories, by which is meant that the direct solar radiation before ab- 

 sorption by the earth's atmosphere would in falling for one minute, nor- 

 mally, upon an area of a square centimeter, raise the temperature of 

 one gramme of water 2°.6 or 3° centigrade. This implies its ability to 

 melt aunuall^' a crust of ice covering the whole earth over 150 feet thick. 

 This amount is one-half greater than the received value of Pouillet, and 

 greater than the latest determinations of Messrs. Crova and Violle." 



On the summit of Mount Whitney an ordinary black-bulb thermom- 



