44 
This explained the equal performance of these objectives, by 
showing that in fact the effective portions of their apertures 
were nearly the same. 
“No. 4. A similar twelfth, but not quite so good, gave for 
the bright part, and for the limit of the radial stripes of light, 
Al = 102°, 0.06 35 Ae 122 in a Ae 
«No. 5. A tenth, said to be of 156°, had the same jagged 
edge of shadows fading to darkness without any definite ter- 
mination; the light stripes were fainter than usual. 
A= 146; oes, ss A= Lobe 
In the usual method light could be seen through 159°, but 
was unbroken only through 115°. 
“No.6. A twelfth, said to be 170°, and in which light was 
seen through 169°, but for much of that arc so streaky, that 
I was prepared to find its performance not quite conformable 
to its aperture, though its workmanship is of the highest order. 
It presented in the solar apparatus the same appearance as 
No. 2, with this exception, that the bright central part was 
not uniform, two-thirds of it being brighter than the rest, and 
the change rather abrupt; three or four of the radial shadows 
were also much broader and blacker than the rest. For the 
clear diameter, 
AP 399° Gre A acrme. Ran LPT Gea 
On looking at this objective, light (and pretty bright too) 
could be seen even at 90°; which induced me to establish 
a second microscope, power 41, and fitted with a shade- 
glass, to examine the image of the sun which was formed in 
the focus of the objective. This image, whose diameter was 
0:0007, was seen through a considerable range as a well-de- 
fined circle; but at last a bright curve, probably the edge of 
one of the cells, was seen to approach it o}) When it came 
into contact with this it became deformed, and increasing the 
