“Royal Society. 387 
In all these different kinds Dr. H. found traces of ammonia and 
azote ; and hence he concludes with Sprengel, that the narcotic 
principle is owing to azote, which is probably combined with 
ammonia. 
May 19. A letter to the President from Dr. Brewster was 
read, mentioning his observations on the effects which heated 
glass produces on light. Dr. B. being engaged in various ex- 
periments of this nature, noticed the effect which wax melted be- 
tween two plates of glass had on light, and was thence induced to 
experiment on the glass properly heated. For this purpose he 
adopted those pieces of glass called Prince Rupert’s drops; he 
ground them with perpendicular and parallel faces, and ‘also at 
right angles ; but he uniformly found that they either wholly or 
partially depolarized light, and that he could not. transmit 
through them a ray of pulverized light without its undergoing 
some modification. 
Mr. Herschel laid before the Society a mathematical paper 
_on Analysis: it was divided into four sections ; but being en- 
tirely algebraical, it was of a nature not adopted for public read- 
ing. 
Captain Cater furnished an account of his additional experi- 
ments on the comparative powers of the Cassegrainian and Gre- 
gotian telescopes. His object was to discover if some error 
might not have crept into his former experiments, and whether 
he was not deceived by some optical delusion, which occasion- 
ally misleads young and sanguine observers. For this purpose 
he caused different persons to examine the appearances: some 
of them knew nothing of the subject of his inquiry, yet all of 
them concurred in the same observation. Nevertheless he ad- 
mits the great liability to errors in such experiments, and cor- 
rects many of the observations by calculation. He made a va- 
riety of experiments with the reflectors, which in general tended 
to prove the superiority of the Cassegrainian over the Gregorian 
telescope. 
May 26. Sir Everard Home, bart. gave an historical sketch 
of the nature and effects of the different injuries of the brain, 
with a view to embody facts so that inquirers and observers might 
more easily direct their researches. Sir Everard did not profess 
to state any new discovery, but merely to relate some cases which 
had occurred in his own practice: he divided his paper into sec- 
tions, each of which describes an injury of the brain, with its 
physical and mental effects.. The first was pressure; and if this be 
either too great or too little, the consequence is violent head- 
aches, vomiting, &c. He next considered the effects of water, 
and related some cases where six beer pints were contained in 
the brain without destroying the vital functions, or the mind. In 
Bb2 other 
. 
