234 Capt. Kater’s further Experiments on the Light 
P. S. A fact which appears to be somewhat analogous to 
that which i have observed, has been remarked by Dr. Brew- 
ster in his late treatise on Philosophical Instruments. “ It is a 
curious fact/' he says, p. 44, “ that the circular images or the 
sections of the cone of rays, are never so distinct and well 
defined after the rays have crossed — as they are before — 
and again, p. 193, “ the sections of the cones of light are, in 
general, better defined, when they are taken between the object 
glass and its principal focus." 
APPENDIX. 
Since the preceding paper was submitted to the Royal Society, 
I have made numerous experiments connected with the same 
subject for the purpose of bringing the results I then deduced 
to the test of a further examination, conducted in a different 
manner, and with a more simple apparatus. 
My object was to determine the intensity of light reflected 
from a concave mirror at equal distances from its focus, and 
thus to decide, in a direct manner, whether any rays are lost 
in crossing each other at the place where an image is formed. 
The mirror employed in these experiments belongs to an 
excellent Newtonian telescope ; its diameter is 4,6, and its 
solar focus 22,5 inches. This mirror was supported by means 
of a cylindrical rod of iron screwed to the back of the cell 
which contains it, on two upright pieces of wood mortised into 
a square board, which thus formed a frame in which the mirror 
might be fixed in any required position. 
