g 6 q Dr. Herschei/s additional Observations , &c. 
Explanation of the Figures. Plate XXVIII. 
A B, Fig. 1, is a square trough, closed at the two opposite 
ends C D, by well polished plain glasses. It will hold any liquid 
through which the sun's rays are to be transmitted. E is a 
small spout, and F a handle, so that any portion of the liquid 
may conveniently be poured out, when the rest is to be diluted. 
The trough is made to fit into the open part of the skeleton 
eye-tube. Fig. 2, resting on the bottom G, and being held in its 
proper situation by the sides H and I. The end K, at the time 
of observation, is put into a short tube fixed to the Newtonian 
telescope, and may be turned about, so as always to have the 
open part H I horizontal. 
When the eye-piece Fig. 3, is screwed, by its end M, into 
the skeleton tube at L, Fig. 2, and the trough Fig. 1 , with any 
liquid to be tried, is placed in the open part G H I, the sun's 
rays will come from the small mirror of the telescope to K, and, 
passing through the plain glasses C D, inclosing the liquid, will 
enter the eye-piece M, and, after the necessary refractions, come 
to the eye at N. 
Any other, single or double, eye-pieces, of different magni- 
fying powers, may be screwed into L, instead of the piece 
Fig. 3 ; and the liquid may easily be tempered so as to inter- 
cept a proper quantity of light to suit every eye-glass which is 
in use, and thus to render the inspection of the sun perfectly 
convenient. 
