■ S. P. Langley — Temperature of the Moon. 433 



that of the moon. The difference is so considerable that even 

 the temperature fluctuations due to the interposition of the in- 

 tervening atmosphere in no case this evening hide the fact. 



In order to compare the fluctuating radiations of the atmos- 

 phere with a constant source, we take the mean of the sky 

 observations and compare it with the mean of the readings on 



il T 4.1. ■ i.- 1 B + D A + E • A't 



the screen. In this particular case, ■ gives a dif- 

 ference of but Q'l division ; but this is, as we have already 

 observed, when the bolometer is directed towards the orange 

 in the luminous part of the spectrum, and our cold screen, it 

 need hardly be said, is not emitting any rays of orange light. 

 We conclude, then, that the apparent deflection of Ol div. 

 here has no real significance ; but, as we go down the spectrum 

 towards the region of the radiations from cold bodies, we find, 

 beyond deviation 39° (^=4 , '"3), values which indicate a real 

 excess of screen over sky radiations. 



We have selected the first number in our second series of 

 Feb. 9, 1887, as the example, because this follows the normal 

 course without marked instrumental disturbance The nature 

 of these fortuitous disturbances and the methods adopted for 

 their correction are explained in the original memoir. In 

 many cases, as will be seen, they may cause the sky on one 

 side or the other of the moon to appear momentarily warmer, 

 although the mean of the two is colder. 



Comparisons of the sky and screen by directing the bolo- 

 meter to the sky at the zenith and at the east and west horizons 

 follow, and three double series at the most important points in 

 the spectrum, made with the moon at a high, a low, and an 

 intermediate altitude, give indications of the atmospheric ab- 

 sorption. These, however, are not given here, but only the 

 double series (No. 2) of which a literal transcript from the 

 book of original entry now follows : 



Station. Allegheny. j Spectrum thrown west. 



Date, February 9. 1887. ! Galvanometer No. 3. 



Wet bulb at 7 h 30 m = + 1 1°-2 C. } T . J Time single vibration=l 2 s . 



Dry bulb at 7 h 30 m =+ 16"-0 C. \ imernal Deflection per degree Centigrade=17-8. 



Temperature apparatus at 9 h 45 m =+ Bolometer No. 1 ; aperture = 3 mm =27 /- 9. 



19°-8 C. Setting on D 2 = 41° 08' 30". 



External temperature, near the freezing Battery current = - 038 ampere. 



point. ; Reader at circle, J. P. 



State of sky at 8 h 30 m clear. Very good Reader at galvanometer, F. W. V. 



sky. 

 Aperture of slit=3 mm = 27 A 9. 

 Prism used L„: A=60° 00' 28". 

 Rock-salt lenses set at 37 cm . 



