PRODUCED BY ELECTRO-CHEMICAL ACTION. 97 
by Newton around the point of contact of two slightly convex glasses or 
lenses. The order of the latter colours should therefore correspond ex- 
actly with that of my scale. It does so in fact; but that the correspond- 
ence may be perceived, it will be necessary first to rectify some errors 
which have arisen respecting the rings of Newton, either in consequence 
of their small dimensions, or of their having been examined under the 
influence of some prejudice. 
Our scale embraces the extent of the first four rings, and consists, as 
we have already stated, of forty-four tints. 
The tints of No. 1 to No. 10 (inclusive) correspond to the Ist ring. 
11 28 2nd — 
29 —— 38 3rd — 
39 —— 44 4th — 
Fundamental Principle. 
It is well known that the colours of the thin layers around the point 
of contact of Newton’s glasses are formed in the following manner. At 
the point which allows all the rays of the transmitted light to pass there 
appears a dark speck, and this remains the same whatever may be the 
quality of the light. If the incident light is white, the central speck is 
succeeded by several irises or concentric rings. If the light is homo- 
geneous or produced by one species of rays, the irises are changed into 
rings of the same colour as the incident rays, and separated from each 
other by dark intervals. These rings, whatever be their colour, have 
their commencement all at the verge of the central speck, but they oc- 
cupy different spaces. The violet rings are the narrowest and nearest ; 
the red are the widest and most distant; the rings of the intermediate co- 
lours are of intermediate dimensions and at intermediate distances. When 
the incident light is white, the series of homogeneous rings are formed 
simultaneously and overlap each other ; all the colours are intermixed in 
different proportions, and none stands isolated. It is to these combina- 
tions that we are to attribute the tints of the thin layers which we are 
about to analyse on our scale. 
First Ring.—From No. 1 to No. 10 (inelusive). 
The Scale commences with the blond* colour: of this there are four 
gradations, the first of which is silvery, and 2, 3, 4 are gradually deeper. 
The blond is succeeded by the tawny. Of this there are three species, 
* [The term blond employed in the original has been retained in-the trans- 
lation to avoid the difficulty of giving an exact equivalent. Those brownish tints 
ch in reference to human hair we term light or fair are evidently intended. 
—Eoir. 
__ ¢ [In the original the name of this colour is fawve, from the Latin fulvus; and 
the author says that he employs it in order to avoid the circumlocution of ‘lion- 
colour’.—Epir. ] 
Vou. I.—Parrt I. 3 H 
