206 Dr. Forster on the Variation of ike infective, 



thing to do with the peculiar tendency of this planet to produce 

 a bad spectrum for observation even in the best telescopes. 

 Out of the consideration of the chroniatopoietic property of 

 the atmospheres of the planets, a question arises, Whether 

 that property be subject to variation ? There is a manifest 

 difficulty in ascertaining this, because the reflected light of 

 the sun passes through our own atmosphere as well as that of 

 the planet; and consequently we cannot always tell to which 

 atmosphere to refer any colour which we may observe in 

 the spectrum. Observations made on two or more planets 

 at once, where the changes in the light of the two or more 

 severally did not correspond, might lead more directly to the 

 solution of this question. But we are getting now away from 

 our object, and must retrace our steps before we wander too 

 far into the wide field of speculation which lies open before 

 us. Observations are as yet wanting to establish and sy- 

 stematize the facts briefly alluded to above ; but it is to be 

 hoped, from the united efforts of numerous astronomers and 

 meteorologists now beginning to be in communication with 

 each other all over the world, that the desiderata, quantum 

 posswit, will be supplied. The present subject affords an 

 example of the natural connection between the two sister 

 sciences, and affords a hope that the many learned men who 

 compose the Astronomical and Meteorological Societies will 

 cooperate in the attainment of a common object, and that 

 the peculiarities and variations of atmospheric refraction will 

 be more fully known than they have been hitherto, by the 

 multiplied observations of individuals acting in concert*. 



Of the Colours, of the Moon. 

 The Moon viewed in the prism seems to possess all the co- 

 lours ; and their proportions, as far as we can judge, are very 

 similar to those observed in Venus. But the observations I am 

 about to make on the lunar disk, are intended rather to confirm 

 a point that I am contending for in meteorology, than to esta- 

 blish the proportion which her component rays of light bear to 



* It appears that the ancients were not inattentive to the different co- 

 lours of the planets. 



Pliny thus distinguishes them; which, though not a very clear description 

 on account of the very promiscuous use of names for colour among the 

 ancients, shows at least that considerable differences in their light had been 

 observed even in his time. In Hist. Nat. lib. ii. cap. 18. we find, "Suits 

 guidem cuique color est; Saturiw candidus, Jovi clams, Marti igneus, Luci- 

 J'ero enndens vespe/i refulgens, Mercurio radians, Luna blandus. Soli cum 

 oritur ardens postea radians." He then goes on to notice the varying co- 

 lours of the same planets and of the Sun at different altitudes and in dif- 

 ferent states of the atmosphere. Of the observations of the ancients I 

 shall say more in a future Number. 



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