254 European Science. [May, 



surface of Jupiter*, which with a density, and therefore a heat-conducting power, 

 even less than those of the sun, has 300 times the earth's weight. 



Popular belief, both in ancient and in modern times, has attributed a frigorific 

 power to the rays of the moon. Modern philosophers, on the contrary, have all 

 expected a calorific effect from the concentration of her beams ; and an American 

 journalist has recently published the alleged result of an experiment, in which an 

 evident rising of the thermometer was occasioned by a powerful arrangement of 

 this kind. Dr. Lardner, in his monogram on heat, published in 1833, calculates 

 on the supposition that the respective heating powers of the sun and moon's rays 

 are in the ratio of their brightness ; that in the experiment of De La Hire, who 

 condensed the lunar rays 300 times by a 3-feet burning glass, the heating ef- 

 fect could not have been so much as 5 l 5 of a degree. Sir John Herschel, in his 

 work (which I have not seen) on Astronomy, also published last year, gives the 

 following imaginary description of the lunar climate : 



" The moon has no clouds, nor any other indications of an atmosphere ; hence its 

 climate must be very extraordinary : the alternation being that of unmitigated and 

 burning sunshine, fiercer than an equatorial noon, continued for a whole fortnight, 

 and the keenest severity of frost, far exceeding that of our polar winters, for an 

 equal time. Such a disposition of things must produce a constant transfer of 

 whatever moisture may exist on its surface, from the point beneath the sun to that 

 opposite, by distillation in vacuo, after the manner of the little instrument called 

 a cryophorus. The consequence must be absolute aridity below the vertical sun, 

 constant accretion of hoar frost in the opposite region, and, perhaps, a narrow 

 zone of running water at the borders of the enlightened hemisphere. It is possible 

 then, that evaporation on the one hand, and condensation on the other, may to a 

 certain extent preserve an equilibrium of temperature, and mitigate the extreme 

 severity of both climates." 



In this instance, popular prejudice, though also overshooting the mark, has 

 probably erred less than philosophical hypothesis. There is no sufficient reason 

 for believing that the moon's temperature ever was higher than that of the earth at 

 the same time ; and on the supposition that at some very distant period they were 

 equal, it must follow from the greater comparatively surface of the moon, from her 

 greater density and heat-conducting probable power, and still more, from her almost 

 total want of an atmosphere, that her temperature on the surface is very greatly in- 

 ferior to that of any portion of the earth ; whence, under any circumstances, the 

 earth must constantly give out heat to the moon, which will, therefore, with effect, 

 appreciable or not, according to the power and sensibility of the instruments em- 

 ployed, act upon the thermometer like the mass of ice used by the Florentine 

 Academicians, which gave rise to so many speculations upon the possibility of a 

 radiation of cold. It is probable that the temperature of the moon's surface does 

 not exceed that of the etherial space which immediately surrounds it ; and, from 

 the considerations above detailed, especially the moon's smaller mass, that this falls 

 short of the temperature determined by Fourier as belonging to the etherial space 

 immediately beyond the earth's atmosphere. 



* The physical condition of Jupiter's surface, his ever -varying belts, all disposed in 

 parallelism with his equator, and the occasional more permanent spots like the sum- 

 mits of icebergs floating in a liquid medium, would perhaps be best explained by the 

 hypothesis of this planet still being in a state of partial fusion. His moons may be 

 at a lower temperature, and now inhabited. 



