335 Upon the variegated Colours of Bodies 



seem to me to be explained very naturally by this method 

 alone. Nevertheless I restrict myself to presenting it as a 

 simple probability. In order to leave nothing further to be 

 desired upon such a proposition, it will certainly be necessa- 

 ry to make a more profound examination of it, and particu- 

 larly to try if we can apply any calculation to it, for the pur- 

 pose of seeing whether, from the double virtue, attractive 

 and repulsive, attributed to each molecule of any body, it 

 would be possible, in a given case, to deduce the movement 

 of the luminous rays reflected, or pushed, sometimes in one 

 direction, and sometimes in another, conformably to the 

 flexions or transmissions operated by the pellicles. 



To conclude, it is more important to the object I have in 

 view to remark, that the colours resulting from the fits of 

 easy reflexions and transmissions, are produced equally, as 

 was clearly seen by Mazeas, between the close connected 

 surfaces of two bodies, without any substance whatever be- 

 ing between them * ; for instance, betvveeh two lenses, or 

 two glasses applied against each other and placed under the 

 exhausted receiver of an air-pump. 



On the other hand, these colours do not always require a 

 very minute separation of surfaces, since Newton himself 

 obtained coloured rings by the action of the two surfaces of 

 a concave glass mirror, three lines in thickness, and found 

 that these rings, with respect to thick plates, depended upon 

 the thickness, following the same law which he had laid 

 down with respect to ihin plates ; and this he again con- 

 firmed by the observation of the rings upon a mirror only 

 07ie line thick f. 



We see therefore, on referring to the various phoenomena 

 I have quoted, that the colours emitted by a pellicle or thin 

 plate of glass, are as fugitive and independent of the colour 

 proper to the substance, as those of a thick mass of glass; 

 that these kinds of culours may not even depend upon the 

 thickness of any substance, as when they arise in the inter- 

 val of two close joined glasses, or in the fissures of certain 

 minerals ; that ihey have the greatest analogy w ith the co- 

 ronrc produced through a fog, a smoke, or in the intervals 



* Memoirs of the Berlin Academy, 1752. f Optics t)oolc ii. part 4. 



of 



