128 Mr Barton's Method of making the 1 ri§ Metal, ornaments ) 
ture to predict, that a time will arrive, when the accumula^ 
ting labour which arises from the arithmetical applications of 
mathematical formulae, acting as a constantly retarding force, 
shall ultimately impede the useful progress of the science, unless 
this or some equivalent method is devised for relieving it from 
the overwhelming incumbrance of numerical detail. I remain, 
My Dear Sir, 
Faithfully yours, 
Devonshire Street, 
Portland Place, 
6 th Nov . 1822. 
Art. XXI. — - Account of Mr Barton's Method of making the 
Iris Metal ' ornaments , or of ornamenting Steel , and other 
Metals , with the Prismatic Colours. 
JL HE production of the prismatic tints, by scratches upon the 
surfaces of metallic and transparent bodies, was first observed 
by the celebrated Boyle. They were particularly studied by 
Mazeas and Mr Brougham ; and Dr Thomas Young after- 
wards examined them with particular care, and ranked them in 
the class of optical phenomena, known by the name of the “ Co- 
lours of striated Surfaces." 
Dr Young's experiments were made on the prismatic colours 
displayed in Mr Coventry’s micrometers, consisting of parallel 
lines drawn upon glass, at the distance of ~ 0 th of an inch. 
Each of these lines he found to consist of two or more finer 
lines, at the distance of somewhat more than ^th of that of the 
adjacent lines. Dr Young ascribes these colours to the inter- 
ference of two portions of light, the one reflected from one side 
of the groove, and the other portion from the other side ; and 
he concludes, that there is a striking analogy between this sepa- 
ration of colours, and the production of a musical note, by suc- 
cessive echoes from equidistant iron palisades. 
This class of colours was afterwards investigated by Dr Brew- 
ster, as exhibited in Mother -of -Pearly and in various other ways. 
He found, by the aid of the microscope, that they arose from 
grooves in its surface ; that they were produced when the flat 
C. Barrage 
