304 DR. BREWSTER ON PERIODICAL COLOURS PRODUCED BY THE 



Number of grooves 

 in an inch. 



2000 on wax. 



2000 on wax. 



2500 



3333 

 5000 



10,000 



Orders and portions of orders of colours developed from 

 90° up to 0° of incidence. 



One complete order, together with greenish yellow of the 



second order. 

 One complete order, together with gamboge yellow of the 



second order. 

 One complete order, together with the full blue of the second 



order. 

 Gamboge yellow of the first order. 

 One complete order, together with bluish white of the second 



order. Colours more dilute than in No. 5. 

 One complete order, together with blue and fainter blue of 



the second order. 



It is obvious from the preceding Table that the diversity of effect produced 

 by different specimens does not depend upon the quantity m + »?, but upon n. 

 The more that the original surface is ploughed away by the cutting diamond, 

 the more brilliant were the tints, and the more numerous the orders of colours. 



I was now desirous of seeing what effect would be produced when the 

 original surface was almost wholly removed ; and Mr. Barton was so obliging 

 as to execute for me a specimen containing 2000 grooves in an inch, in which 

 this was nearly effected. His diamond point, however, having unfortunately 

 broken before he had executed any considerable space, I was unable to make 

 all the experiments with it which I could have wished. 



This specimen produced four complete orders of colours, all of which were 

 developed at much greater angles of incidence than those in the preceding 

 Tables. 



White 



Straw yellow. 



Faint red. 



Pink. 



First limit of pink and blue 



Blue. 



Green. 



Yellow. 



90 00 



80 00 



Red. 



Pink. 



Second limit of pink and blue 69 40 



Blue. 



Green. 



Yellowish green. 



Yellow. 



Orange. 



