AJlernaling Colours of Stars. 393 



The Upper Missouri country is in the same latitude as England; 

 its winters are a little more rigorous and its summers somewhat 

 warmer ; and it abounds in rich pastures of white trefoil, which 

 the hunters call Buflalo grass. 



From what has been stated, we find that these animals were ex- 

 hibited as curiosities even in the principal American cities, con- 

 sequently they must be unknown in all the cultivated and settled 

 parts of the United States. 



ALTERNATING COLOURS OF STARS. 



To Mr. Tilloch. 



Sir, — I HAVE lately made an c(bservation on the rapid mu- 

 tation of the colour of the light of some of the fixed stars, which 

 I think worth noticing in your Magazine, in order principally to 

 induce other persons to l)e attentive to the circumstance. The 

 first observation of this kind I made was in the month of Sep- 

 tember, in a warm evening. In a star of the first magnitude I 

 noticed a rapid alternation in the colour of the light. The change 

 was from the ordinary colour to a deep red, and then back again 

 to the common colour of the star. From repeated observations 

 1 found the red colour to last about two seconds, and the or- 

 dinary colour about three seconds. 



That peculiar apparent motion in the light, commonly called 

 twinkling, was very strong at the time. I observed this ph?e- 

 nomencn during the space of above fifteen minutes, when a cloud 

 obscuring the sky I could no longer see it. I attributed this to 

 the refraction produced by some terrestrial vapour which might 

 be rising up in undulatory or intercepted layers, and had no idea 

 at the time of the possibility that it might depend on the man- 

 ner of the transmission of light from the star, till I noticed it 

 again this month in the « Orionis, when the reddish colour agaia, 

 alternated with the yellowish, and the alternation was more rapid 

 and corresponded to the twinkling. 



I have merely noticed this circumstance here in a hasty and 

 cursory manner, to excite others to observe, as I have always no- 

 ticed it in autumn. But I hope shortly to lay before the public 

 more accurate miimtes of observations on this phsenomenon. 

 Without offering any further comment on its possible cause at 

 present, 1 am, in haste, yours, &c. 



Clapton, Oct. 16, 1816. . TlIOMAS FoRSTER. 



P. S. — If any corresponding observations have been made in 

 distant countries, I .sliiill be obliged Ijy their communication 

 through your Magazine. 1 hope, with vour permission, in a 

 hiture number to give minutes of some of my observations which 

 I liave not by me at present. 



TELLU. 



