( 376 ) 



oil is to be considered, and this is mucli smaller than the 

 difference bctwccn air aiid water. 



It appears to be necessary for the productiou of thep(^ 

 colours, that the glasses be held nearly in a right line be- 

 tvveen the eye and the common termination of a dark and 

 lumineus object ; the portion of the rings, seen on the 

 dark ground, is then more dislinct than the reiiiaining por- 

 tion ; and, instead of beiug continuations of the riugs, they 

 exhibit every where opposite colours, so as to resemble 

 the colours of coramon thin plates seen by reflection, and 

 not by transniission. 



In order to understand this circumstance, we must oon- 

 sider, that where a dark object (as A fig. 1) is placed be- 

 hind the glasses, the whole of the light, which comes to 

 the eye, is either refracted through the edges of the drops, 

 (as the rays B,C',) or reflccted from the iuternal surface (as 

 D,E ;) while the light, which passes through those parts of 

 the glasses which are on the side opposite to the dark ob- 

 ject, oonsists of rays refracted as before through the edges, 

 (as E, G,) or simply passing through the fluid (as H, I.) 

 ïhe respective combinations of these portions of light exhibit 

 series of colours in dill'erent orders, since the iutemal re- 

 flection modifies the interferonce of the rays on the side of 

 the dark object, in the same manner as in the common 

 colours of thin plates, seen by reflection. When no dark 

 object is near, both these series of colours are produced 

 at-once; and since they are always of an opposite nature 

 at any given thickness of a plate, they neutralise each 

 ether, and constitute white light." 



&. Na YOUNG heeft de Heer babinet in geschrifte over 

 dit onderwerp gehandeld in eenen brief aan ar.igo *) ; ook 



•) CoMpIcs Rendtis, 1839, Vol. VIII. p. 306 et 307 



