37° Mr. Brougham's Experiments and Observations 
i. e. their axes are proportional. I now could produce what 
spots I pleased, by gently scratching the speculum, or by mak- 
ing lines, dots, &c. with ink, and allowing it to dry ; for these 
last formed convex fibres, which produced coloured fringes as 
well as the concavities, agreeably to what was deduced a 
priori. 
Observation 7. The whole appearance which I have been de- 
scribing bore such a close and complete resemblance to the 
fringes made round the shadows of bodies, that the identity of 
the cause in both cases could not be doubted. In order how- 
ever to shew it still further, I measured the breadths of two 
contiguous fringes in several different sets ; the measurements 
agreed very well, and gave the breadth of the first fringe .00 56, 
and of the second .0034; or of the first .0066, and of the second 
.0034,. The ratio of the breadths by the first is 28 to 17; by 
the second 30 to 17; of which the medium is 29 to 17, and this 
is precisely the ratio of the two innermost fringes made by a 
hair, according to Sir Isaac Newton's measurement : the first 
being, according to him, of an inch ; the second 
an inch.* Farther, the two innermost rings made by plates 
have their diameters (not breadths) in the ratio of to 2f-f, 
and the distance between the middle of the innermost fringes 
(made by a hair), on either side the shadow, is to the same 
distance in the second fringes as to therefore the diame- 
ters of the two first rings made by the specks in the speculum, 
are as |-§|- to -piiz 5 which ratio differs exceedingly little from 
that of 14-J to 2J-, the ratio of the diameters of rings made by 
plates, either those called by Newton thick, or those which 
• Optics, Book 3. Obs. 3. + Book 2. Parts 1 and 4. 
