NATURAL PHILOSOPHY. 135 



those under the red ray. Frogs placed in a dark chamber lose one-half less 

 of moisture by evaporation, than when placed in common daylight. 



OX MOLECULAR IMPRESSIONS BY LIGHT AND ELECTRICITY. 



The following is an abstract of a paper on the above subject recently read 

 before the Royal Institution, London, by Mr. Grove : 



The term molecular is used in different senses by different authors. It is 

 used in the present connection to signify the particles of bodies smaller than 

 those having a sensible magnitude, or as a term of contradistinction from 

 masses. If there be any distinctive characteristic of the science of the pres- 

 ent century, as contrasted with that of former times, it is the progress made 

 in molecular physics, or the successive discoveries which have shown that 

 when ordinary ponderable matter is subjected to the action of what were 

 formerly called the imponderables, the matter is molecularly changed. The 

 remarkable relations existing between the physical structure of matter, and 

 its effect upon heat, light, electricity, magnetism, etc., seem, until the present 

 century, to have attracted little attention: thus, to take the two agents 

 selected for this evening's discourse, Light and Electricity, how manifestly 

 their effects depend upon the molecular organization of the bodies subjected 

 to their influence. Carbon in the form of diamond transmits light but stops 

 electricity. Carbon in the form of coke or graphite, into which the diamond 

 may be transformed by heat, transmits electricity but stops light. Leonard 

 Euler alone conceived that light may be regarded as a movement or undula- 

 tion of ordinary matter; and Dr. Young, in answer, stated as a most formid- 

 able objection, that if this view were correct all bodies should possess the 

 properties of solar phosphorus, or should be thrown into a state of molecular 

 vibration by the impact of light, just as a resonant body is thrown into 

 vibration by the impact of sound, and thus give back to the sentient organ 

 an effect similar to that of the original impulse. In the last edition of his 

 "Essay on the Correlation of Physical Forces " (1855), Mr. Grove has made 

 the following remarks on this question: "To the main objection of Dr. 

 Young that all bodies would have the properties of solar phosphorus if light 

 consisted in the undulations of ordinary matter, it may be answered that so 

 many bodies have this property, and with so great variety in its duration, 

 that non constat all may not have it, though for a time so short that the eye 

 cannot detect its duration." The above conjecture has been substantially 

 verified by the recent experiments .of M. Xiepce de St. Victor, of which the 

 following is a short resume: An engraving which has been for some time 

 in the dark is exposed to sunlight as to one half, the other half being covered 

 by an opaque screen : it is then taken into a dark room, the screen removed, 

 and the whole surface placed in close proximity to a sheet of highly sensitive 

 photographic paper, the portion upon which the light has impinged is repro- 

 duced on the photographic paper, while no effect is produced by the portion 

 which had been screened from light : white bodies produce the greatest effect, 

 black little or none, and colors intermediate effects. Mr. Grove had little 

 doubt that had the discourse been given in the summer instead of mid-winter, 

 he could have literally realized in this theatre the Laputa problem of extract- 

 ing sunbeams from cucumbers ! While fishing in the grounds of M. Seguin, 

 at Fontenay, Mr. Grove observed some white patches on the skin of a trout, 

 which he was satisfied had not been there when the fish was taken out of the 

 water. The fish having been rolling about in some leaves at the foot of a 



