36 MEMOIKS OF THE NATIONAL ACADEMY OF SCIENCES. 



The followiug observations were obtained: 



One hundred and seventy-six divisions was therefore taken as the deflection produced by the 

 sun at apparent noon, when bis zenith distance was 62° 43'. 



On drawing a smooth curve through points given by the lunar observations in the first table 

 we find that the deflection produced by the moon at the same zenith distance was 245 divisions. 

 On the evening of December 2 the moon's geocentric semi diameter was 16' 47", and the semi, 

 diameter at the time and i)lace of observation was 16' 55". The focal length of the concave mirror 

 being 73.4 centimeters and the diameter of the moonbeam 20.3 centimeters, the concentration of 

 the moonlight was 



(20^)1 (^?I'_7qn ^ 



(73.4 + sin 16' 55"Y-{.722f- '^^''^ 



The aperture through which the sunlight was admitted was 0.486 centimeter diameter, and 

 the bolometer strips, when exposed, were distant from it 653.5 centimeters. The sun's semi-diam- 

 eter at noon being 16' 16".5, the approximate diminution of solar light and heat was 



(«-*««)^ ^__(0A86): .00530 



(653.5 X sin 16' 16".5f (6.674f 



The moon was not quite full atthe time of observation. We find by Zollner's formula that if it had 



245 

 been, the deflection produced would have been -wtv =272 div. We have, then, for the observed ratio 



of radiation from the full moon to that of the sun, both bodies being at a zenith distance of 62° 43', 



272 1 J, 530 ^ 1^ 

 176^790.5 100,000 96509 



values which the reader is again reminded are presumably subject to large constant errors. The 

 maximum total heat which we can by possibility receive from the moon, even in the absence of an 

 absorbing atmosphere, as is shown elsewhere, is about 1-97000 of the solar heat. It is improbable 

 that such a coincidence as that presented with the observed value just given is other than largely 

 the result of chance, or rather of such constant errors tending in an unknown degree to increase 

 the observed values. 



Class 2. — Comparison of the heat from the moon with that from a Leslie cube. 



On December 3, 1884, the temperature of the room being 0° C, the bolometer was exposed to 

 the radiation from a Leslie cube filled with boiling water, which was observed through the circular 

 aperture of a screen subtending the same angle as the cone of rays from the concave mirror used in 



