A PROBLEM rw OPTICS. 205 
from the outer edge of one, to the outer edge of the other 
17', 45". In the firft cafe I had a fine blue ftreak in the 
middle of the object, and in the laft a red ftreak. The 
other lines were too faint, when feen through the telefcope, 
to meafure the angles they fubtended with accuracy, but 
from fuch trials as I made I am fatisfied that from the fe- 
cond line on one fide to the fecond on the other fide, and 
fo on, they were double, triple, quadruple, &c. of the firft 
angles. 
It appears then that a very confiderable portion of the 
beam of light pafled between the hairs, without being at 
all bent out of its firft courfe; that another fmaller porti- 
on was bent at a medium about 7’, 45" each way; the 
red rays a little more, and the blue rays a little lefs; an- 
other ftill fmaller portion 15’, 30”; another 23’, 15”, and 
fo on. But that no light, or next to none, was bent in any 
angle lefs than 6’, nor any light of any particular colour, 
in any intermediate angle between thofe which arife from 
doubling, tripling, &c. of the angle in which it is bent 
in the firft fide lines. 
I was furprized to find that the red rays are more bent 
out of their firft direGtion, and the blue rays lefs; as if the 
hairs aéted with more force on the red than on the blue 
rays, contrary to what happens by refraction, when light 
pafles obliquely through the common furface of two dif- 
ferent mediums. It is, however, confonant to what Sir 
Ifaac Newton obferves with refpe&t to the fringes that 
border the fhadows of hairs and other bodies ; his words 
are, “ And therefore the hair in caufing thefe fringes, 
“« a&ted alike upon the red light or leaft refrangible rays 
“‘ at a greater diftance, and upon the violet or moft re- 
“ frangible rays at a lefs diftance, and by thofe actions 
« difpofed the red light into larger fringes, and the violet 
*¢ into {maller fringes.” 
By purfuing thefe experiments it is probable that new 
and interefting difcoveries may be made, refpecting the 
Dd properties 
