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 + n, 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 90 00 
Straw yellow. 
Faint red. 
Pink. 
First limit of pink and blue . 30 00 
Blue. 
Green. 
Yellow. 
Pink. 
Second limit of pink and blue 69 40 
Blue, 
j Green. 
i Yellowish green. 
Yellow. 
Orange. 
