— 
IL Description of a New Darkening Glass for Solar Observa- 
tions, which has also the property of polarising the whole 
of the transmitted Light. By Davin Brewster, LL. D- 
F. R. S. Lonp. & Enix. & F. A.S. Ev. 
[Read 1st May 1815.] 
T will be readily admitted by every person who has been 
accustomed to solar observations, that an apparatus for di- 
minishing the intensity of the sun’s light, without distorting 
or colouring the resulting image, is still a desideratum in Prac- 
tical Astronomy. 
Dr Herscuet is the only person who has given any degree 
of attention to this subject. When he applied his powerful 
telescopes to examine the surface of the sun, he found that the 
ordinary method of attenuating the light by smoked or colour- 
ed glasses, was of no avail; and it was in the prosecution of his 
experiments for determining the relative advantages of differ- 
ently coloured glasses, or of combinations of differently colour- 
ed glasses, that he was conducted to those splendid discoveries 
respecting the invisible rays, which have formed an epoch both 
in Chemistry and Optics. : 
Vou VAL. Tt D The 
