138 Royal Socle It/. 



N. B. One degree on the theVmometer of Reaumur 13 

 equal to If on that of Celsius, or the Cenlii^rade ; and to 

 2| on those of Fahrenheit, and Walker : hence it follows, 

 that every four tk decimal, on the thermometer of Reaumur, 

 is comcidcnt with every JiJ'tli decimal, on that of Celsius, 

 or the Centigrade ; and with every ninth decimal, on that 

 of Walker; the decimals of F. beini;; each, onepoint, lower 

 than those of W. — Attention to these circumstances will 

 ever serve to regulate this table. — The second column is a 

 continuation of the first. 



The scale commences at the hoiling point of water, and 

 terminates at the greatest degree of cold, art has hitherto 

 produced. M.T. is mean temperature; viz. that tempera- 

 ture at which the human body, in a state of health, and at 

 rest, is unconsious of either heat or cold. 



For a comparative account of these four thermometers, 

 see Phil. Mag. for June 1810, p. 41fi. 



XXIII. Proceedings of Learned Societies, 



ROYAL SOCIETY. 



Jan. 28. X HE Right Hon. President in the chair. A 

 letter from Dr. Brewster to Sir Humphry Davy was read, 

 announcing some Important discoveries in .the double re- 

 fraction and dispersing powers of several substances, as 

 agate in a thin plate about l-15th of an inch thick; chro- 

 Riate of lead, sulphur, fluor spar, Iceland spar, 8cc. The 

 first two r)f these minerals, it appears, exceed the diamond 

 in double refraction and also in dispersion. Dr. Brewster 

 refers to the experiments of Mains on colours, and expresses 

 a hope that his own discoveries in this difficult branch of 

 science may lead to some correct theory of light: but he is 

 still pursuing his experiments, which are not yet in a state 

 ■for generalization. 



Feb. J. Sir Charles Blagden communicated a fehort 

 paper on Near-siohtedness, confirming the observations of 

 Mr. Ware, that the early use of concave glasses contributes 

 to iiijure the i.ight. Sir C. stated his own case, being like 

 Mr. VV. near sighted : this he discovered when only nine 

 years old, and used watch-glasses to aid his sight : at length 

 rcquirinir proper glasses, afthe age of 30 he used No. 2 ; a 

 few years after he found it necessary to adopt No. 5, in 

 order to obtain a clear view. Since that period his sight 

 has remained stationary ; but he is inclined to think that 

 had he abstained from the use of glasses, it would have be- 

 come sufficiently long and clear by exercise^ — such is the 



facilitv 



