the dislocation of those rings, and to determine its peculiar cha- 

 racter, as indicated by the direction in which the dislocation takes 

 place ; the protrusion of the alternate quadrants appearing, in cer- 

 tain cases, in one direction, and in others in the opposite. These 

 observations are reducible to two classes ; first, those designed to 

 contribute to the inquiry, what substances possess the property of 

 elliptic polarization, by examining the light reflected from various 

 bodies ; and second, those made on certain cases of films of several 

 kinds, including those formed on metals by oxidation or other action 

 upon the metal itself, as well as by extraneous deposition. The 

 author found the general result, in all these cases, to be, that from 

 any one tint to another, through each entire order of tints, the form 

 of the rings in the reflected light undergoes certain regular changes; 

 passing from a dislocation in one direction to that in the opposite, 

 through an intermediate point of no dislocation, or of plane polar- 

 ization ; and thus exhibiting a dark and a bright centred system 

 alternately, as long as the order of tints are preserved pure. These 

 changes in the form of the rings, he observes, are precisely those 

 expressed by successive modifications of Mr. Airy's formula, corre- 

 sponding to the increments in the retardation which belong to the 

 periodical colours of the films. 



The remaining portion of the paper is occupied by a description 

 of the apparatus and mode of conducting the experiments ; and of 

 the observations made on mica, on decomposed glass, plumbago, 

 daguerreotype, and other metallic plates, and on the coloured films 

 produced on steel and on copper by the action of heat, and of voltaic 

 electricity. The author gives, in conclusion, an analytical inves- 

 tigation of Mr. Airy's general formula. 



2. " Variation of the Magnetic Needle as observed at Washing- 

 ton City, D. C, from 3^ SO"* July 24th to 3^ July 25th, 1840, in- 

 clusive (Gottingen mean time)," by Lieut. Gillies, of the United 

 States Service. Communicated by Samuel Hunter Christie, Esq., 

 Sec. R.S. 



February 2, 1843. 



Sir JOHN WILLIAM LUBBOCK, Bart., V.P. and Treasurer, 

 in the Chair, succeeded by the MARQUIS OF NORTHAMP- 

 TON, the President, in the Chair. 



John Benjamin Heath, Esq., James MacCullagh, Esq., and George 

 Owen Rees, M.D., were balloted for and duly elected Fellows of 

 the Society. 



A paper was read, entitled " Experimental Researches in Electri- 

 city :" Eighteenth Series ; by Michael Faraday, Esq., D.C.L., F.R.S. 

 Section 25. On the Electricity evolved by the Friction of Water 

 and Steam against other bodies. 



