224 Proceedings of Philosophical Societiei^ [MA&fctf, 



a comparison which he has lately had an opportunity of making 

 with some fresh-boiled barometers of Prof. Schumacher, his 

 own guarded barometer, which has been made about fifteen 

 months, and was formerly in perfect accordance with the Royal 

 Society's standard, agreed perfectly with the new instruments, 

 but stood higher than the standard ; and this result was confirmed 

 by a comparison with another barometer belonging to Mr. New- 

 man. The author remarks that it is true the difference of '006 

 inch is but small, but that the depression is as much as could 

 have been expected, and that the whole number of observations 

 being consistent gives weight to the conclusion. 



Mr. D. next brings forward some highly curious observations of 

 Dr. Priestley, which not only confirm his own opinions, but esta- 

 blish the accuracy of Mr. Faraday's observations upon the escape 

 of gases from glass vessels, in which he had attempted to confine 

 them by mercury, and their preservation by water, under similar 

 circumstances, which the author remarks, has been very unneces- 

 sarily called in question. Dr. Priestley found, in his experiments 

 upon air, that when he was operating with mercury, atmospheric 

 air obtained admission into his jars even when there was an inch 

 of mercury on the outside, and a column of two or three inches 

 within ; and he remarks that this is owing to there being no complete 

 contact between mercury and glass, and that the air which is 

 confined between the two is continually protruded forward by 

 the vibrations of the vessel. He also observed that when a little 

 water was placed upon the outside of the jar upon the mercury, 

 that neither air nor water ever got in to disturb his experiments. 



The paper concluded with a brief and connected view of the 

 author's observations upon the barometer derived from the pre- 

 sent communication, and from two former papers, which, he 

 observes, the Council have done him the honour to place amongst 

 their archives, from which it appears that he has established the 

 following facts : — 



1. That air gradually insinuates itself into the best made 

 barometers of the common construction. 



2. That this does not take place from any solution of the air 

 by mercury. 



3. That the passage of the ay: is between the mercury and the 

 glass. 



4. That the gradual deterioration of barometers may be pre- 

 vented by a ring of platinum cemented to the open end of the 

 tube. 



Feb. 2. — A paper was read. On the Magnetizing Power of 

 the more refrangible Rays of Light; by Mrs. Mary Somerville : 

 communicated by William Somerville, MD. FRS. 



In this paper, Mrs. Somerville first mentions some preceding 

 statements on the subject: Prof. Morichini, of Rome, annouriced 

 that he had succeeded in magnetizing a needle by exposing it to 



