NATURAL PHILOSOPHY. 159 



bj a thermometer placed in her immediate vicinity, and affected by the 

 moon (in the assumed absence of an atmosphere) only by her direct radiation. 

 "We have not the means of determining what this temperature may be. 



HEAT OF THE SUN's KAYS. 



At the Albany Meeting of the American Association, Judge Foot read a 

 paper on the heat of the sun's rays, as determined by experiment. He com- 

 menced by a discussion of the proper mode of measuring the heating power of 

 the ray. He had repeated some of the experiments of Cavendish, and had 

 come to the conclusion that ihe true measure could be obtained by adding to 

 the difference of temperature in the sunlight and in the shade a correction for 

 increased temperature in the air. His first result was that the heating power 

 of the sun's rays is not uniform, but varies constantly with the temperature 

 of the place into which the rays fall. He then gave an account of experi- 

 ments with a burning glass, which confirmed this result the heating power 

 of" the focus not varying with the temperature of the glass, but of the place 

 where the focus formed. Furthermore, he thought he had proved that the 

 temperature of air is raised by sunshine passing through it. He found that of 

 two jars of heated air, one placed in the sunlight would retain its heat 

 the longest. Heat did not come from the sun, but light capable of exciting 

 heat. 



Prof. Henry then read a paper by Mrs. Eunice Foote, prefacing it with a 

 few words, to the effect that science was of no country and of no sex. The 

 sphere of woman embraces not only the beautiful and the useful, but the true. 

 Mrs. Foote had determined, first, that the action of the rays increases with 

 the density of the air. She has taken two glass cylinders of the same size, 

 containing thermometers. Into one the air was condensed, and from the 

 other it was exhausted. When they w r ere of the same temperature the cylin- 

 ders were placed side by side in the sun, and the thermometers in the con- 

 densed air rose more than twenty degrees higher than those in the rarefied air. 

 This effect of rarefaction must contribute to produce the feebleness of heating 

 power in the sun's rays on the summits of lofty mountains. Secondly, the 

 effect of the sun's rays is greater in moist than in dry air. In one cylinder 

 the air was saturated with moisture, in the other dried with chloride of lime ; 

 both were placed in the sun, and a difference of about twelve degrees was 

 observed. This high temperature of sunshine in moist air is frequently 

 noticed ; for instance, in the intervals between summer showers. The isother- 

 mal lines on the earth's surface are doubtless affected by the moisture of the 

 ah* giving power to the sun, as well as by the temperature of the ocean yield- 

 ing the moisture. Thirdly, a high effect of the sun's rays is produced in 

 carbonic acid gas. One receiver being filled with carbonic acid, the other 

 with common air. the temperature of the gas in the sun was raised twenty 

 degrees above that of the air. The receiver containing the gas became very 

 sensibly hotter than the other, and was much longer in cooling. An atmo- 

 sphere of that gas would give to our earth a much higher temperature ; and 

 if there once was, as some suppose, a larger proportion of that gas in the air, 

 an increased temperature must have accompanied it, both from the nature of 



