3S+ Dr. Forster on the dispersive Potter 



The colour in the second column is merely the genera, 

 appearance of the star as to colour when viewed in the man- 

 ner already described, before the rays meet in a focus in the 

 telescope ; and is of no particular utility, otherwise than by re- 

 minding the reader of thegeneral varieties of colour of stars. 



I have not detailed the peculiarities of the coloured spectra, 

 from want of time, and because the detail would take up too 

 much space in your valuable Magazine. But I have given 

 the results, as nearly as I could estimate them, in column 3. 



The following seems to be the order of the refrangibility of 

 the planets : but I have not been enabled to state any propor- 

 tions, as the principal method employed to disperse the light 

 of the stars will not disperse that of planets. 



Thus the Moon requires the most, and Mars the least cor- 

 rection for refraction. 



I shall conclude this paper with some miscellaneous ob- 

 servations on a mode of producing colours by vibration of 

 the telescope ; merely to show that by almost any means that 

 we employ to separate the rays of starlight, the results show 

 that stars differ from each other essentially in the composi- 

 tion of their light, and that there is a correspondence in the 

 results, of experiments of very different sorts ; so that what 

 we perceive is a real and not an imaginary difference. 



In a future paper I hope to present you with some curious 

 observations on extraordinary or special refractions, which 

 have happened occasionally in consequence of remarkable at- 

 mospheric changes. I shall also send for a future Number, 

 a Catalogue of Stars, on which no accurate observation can 

 be made on their proportional refraction, and the causes why 

 we cannot make them ; as for example, Algol, Castor, Antares, 

 and others. I write my observations hastily, and from my 

 first impression of the subject, in order that I may induce 

 others to observe and obtain information either in corrobora- 

 tion or refutation of my notions. 



Vibration 



