12$ 



J I is experi- 

 Inents led to 



hew conclusi- 

 ons, and discri- 

 minations. 



Minute detail 

 necessary. 



*Ferm modifi- 

 cation. 



HKRSCIIEL ON COLOURED KINGS* 



tnany times interrupted by astronomical pursuits, has ofterl 

 been taken up again, and has lately been carried to a very 

 considerable extent. The conclusions that may be drawn 

 from them, though they may not perfectly account for all 

 the phenomena of the rings, are yet sufficientl)- well sup- 

 ported, and of such a nature as to point out several modifi- 

 cations of light that have been totally overlooked, and others 

 that have never been properly discriminated. It will, there- 

 fore, be the aim of this paper to arrange and distinguish the 

 various modifications of light in a clear and perspicuous or- 

 der, and afterwards to give my sentiments upon the cause 

 of the formation of the concentric rings. The avowed in- 

 tricacy of the subject*, however, requires, in the first place, 

 a minute detail of experiments, and afterwards a very gra- 

 dual developement of the consequences to be deduced from 

 them. 



As the word modification will frequently be used, it may 

 not be amiss to say, that when applied to light, it is intended 

 •to stand for a general expression of all the changes that are 

 made in its colours, direction, or motion: thus, by the mo- 

 dification of reflection, light is thrown back; by that of re- 

 fraction, it is bent from its former course; by the modifica- 

 tion of dispersion, it is divided into colours, and so of the rest. 



I. Of different Methods to make one set of concentric Rings 

 visible. 



One set of rings 

 made visible 

 by different 



methods. 



In the beginning of my experiments 1 followed the New- 

 tonian example, and, having laid the two object-glasses of 

 Huygens upon one another, I soon perceived the concentric 

 rings. It is almost needless to say, that I found all the 

 Newtonian observations of these rings completely verified ; 

 but as his experiments seemed to be too much confined for 

 drawing general conclusions, I endeavoured to extend them : 

 and by way of rendering the methods I point out very clear, 

 I have given one easy particular instance of each, with the 

 addition of a generalization of it, as follows: 



First Method, On a table placed before a window I laid 



down a slip of glass, the sides of which were perfectly plain, 



neof<dai. parallel, and highly polished. Upon this I laid a double 



* Newton's Optics, 4th ed. p. 288$ end of Obs. 12. 



convex 



-1st method. 

 Double eon 

 vex lens on a 



