144 TWINKLING OF 



variations in its rarity or density ;* and this opi- 

 nion appears to be well founded ; several facts, 

 directly tending to corroborate it, having fallen 

 under my own observation, when engaged in 

 meteorological pursuits. 



A moderate share of attention to the sub- 

 ject is sufficient to convince every thinking man, 

 that the tremulous motion, so evident in the 

 light of the stars, must depend upon mutations 

 which take place in the atmosphere immedi- 

 ately surrounding our globe; for it is allowed 

 to be much more conspicuous at some periods 

 than at others, and in stars elevated from ten 

 to fifty degrees above the horizon than in those 

 nearer the zenith: the planets also, particularly 

 Venus and Jupiter, when their altitude does 

 not exceed fifteen or twenty degrees, are some- 

 times seen to twinkle very perceptibly. It is 

 acknowledged likewise, that, under similar cir- 

 cumstances, stars of the first magnitude, as Siri- 

 us, Arcturus, &c., always twinkle more than 

 smaller ones; stars whose light is white, than 

 those whose light is red ; and that changes in the 

 colour and intensity of their light, frequently 

 accompany this phenomenon. 



* Micrographia, p. 2311 et seq. 



