322 Proceedings of Philosophical Societies, [Marc% 



rency. This nebulous appearance Dr. Brewster is at present 

 examining, hoping that it will throw additional light upon this 

 curious but intricate subject. 2. On the Double Refraction of 

 Chromate of Lead. Dr. Brewster found that the double refran- 

 gibility of chromate of lead is nearly three times as great as that 

 of Icciand crystal. 3. Power of different Bodies to refract Light, 

 Since Newton's time it has been conceived that the diamond 

 possesses this power in the highest degree ; but Dr. Brewster has 

 found that both chromate of lead, and realgar, exceed it consi- 

 derably in this respect. 4. Double Dispersive Power of Bodies, 

 Dr. Brewster has found that bodies possess two different disper- 

 sions, one considerably greater than the other. This he disco- 

 vered at first, by comparing his own measurement of the disper- 

 sive power of a Ijody with that of Dr. Wollaston. 



On Thursday, the 4th February, a paper by Sir Charles 

 Blagden was read, as an appendix to Mr. Ware's observations 

 on short-sightedness. Sir Charles's own experience confirmed 

 Mr. Ware's conclusions. When a boy of four years he was not 

 short-sighted ; but he was so, in a slight degree, at nine. He 

 did not use glasses till 30. At first number 2 answered ; then 

 lie required number 3 ; and at present the glass which he uses is 

 number 5. He thinks that his short-sightedness has been in- 

 creased by the use of glasses, and considers it as probable that if 

 he had not employed glasses it would have gone off altogether. 



At the same meeting was read an account of the late eruption 

 of the volcano called the SufFriere, in the island of St. Vincent, 

 by Mr. Hamilton, of Nevis, in the West Indies. This mountain 

 is the highest, and farthest north, of a chain of mountains which 

 runs through the island. Its height is 3000 feet. It had been 

 famous for its eruptions in former times ; but none have occurred 

 since 17 18. The crater on the top was a mile in diameter, of 

 the form of an inverted cone, and about 800 feet deep. In the 

 middle of it was a conical hill, covered with wood, except the 

 top. The mountain was covered with wood. It got its name 

 from the general quantity of sulphur upon it. Through some of 

 these sulphureous deposites a white smoke was always seen to 

 issue. Some smoke also issued from the little conical hill at the 

 bottom of the crater. The great number of earthquakes, no 

 fewer than 200, during the course of 1811, announced that the 

 entrails of the mountain were in a state of great commotion ; 

 but it continued to be visited by the curious ; and even so late as 

 the 27th of April, a party of gentlemen went to it, and spent 

 several hours in examining the crater. On the 28th the eruption 

 began by a prodigious shower of ashes, which continued to be 

 thrown up all day, and which darkened the air, and loaded the 

 wings of the birds to such a degree as to bring them to the 

 ground. On the 30th, flames were first seen to issue out, ac- 



