1858.] Molecular Impressions by Light and Electricity 463 



the recent progress of science teaches us to look for the reciprocal 

 effects on the matter affected by them. 



Gases which liave transmitted light are altered; as, for example, 

 chlorine is rendered capable of combining directly with hydrogen ; 

 liquids are altered, peroxalate of iron is chemically changed, and 

 gives off carbonic acid ; and the light which has produced these 

 effects is less able to produce them a second time. Solids are 

 altered, as shown in the extensive range of photographic effects. 

 So with electricity, — compound gases are changed chemically, as 

 ammonia or atmospheric air ; elementary gases are changed allo- 

 tropically, as phosphorus vapour, or oxygen ; liquids are changed, 

 as in the decomposition of water and other electrolytes ; and solids 

 are changed, as in the projection of the particles of the terminals, 

 and the impressions on the surfaces of electrics, shown this evening. 

 Frictional electricity may itself be due to the rupture of cohesion 

 between dissimilar molecules ; at all events few, if any, electrical 

 effects have not been proved to be accompanied with molecular 

 changes; and we are daily receiving additions to those produced 

 by light. So, again, iron, and other bodies, have their molecular 

 structure changed by magnetism. Chemical affinity is universally, 

 and heat generally, admitted to be an affection of ordinary matter. 

 Mr. Grove feels deeply convinced that a dynamic theory, one which 

 regards the imponderables as forces acting upon ordinary matter 

 in different states of density, or as modes of motion, and not as 

 fluids or entities, is the truest conception which the mind can form 

 of these agents ; but to those who are not willing to go so far, 

 the ever increasing number of instances of such molecular changes 

 affords a boundless field of promise for future investigation, for 

 new physical discoveries and new practical applications. 



The permanency of such changes also gives valuable means of 

 reading, in the present state of matter, its past history ; final or 

 absolute knowledge on such subjects we cannot hope to obtain, but 

 relative or approximate knowledge is as unlimited as is the degree 

 of improvement in the powers attainable for its acquisition. 



Note. — Since the above was written, the author has observed a 

 case of molecular action which, in some respects, goes further than 

 any yet recorded. lie happened to procure a small Galilean tele- 

 scope, or perspective glass, by DoUond, 6^ inches focus, and l^tlis 

 aperture, of which the tripod stand was so arranged as to fold up 

 and pack into the tube. When so packed it terminated opposite the 

 object glass in a disc of brass, in the centre of which was an aper- 

 ture 3^ths of an inch diameter, and in the centre of this the end of 

 an iron screw, of y^oths of an inch. The distance of the perforated 

 disc from the inner surface of the object glass was Jth of an inch. 

 The impression of this disc and of the central pivot was delicately 

 etched on the glass; the polished surface being disintegrated 

 opposite the brass and iron, an annulus, opposite the space between 



