460 W. B. Grove, Esq. on [Jan. 29, 



phosphorescent force, and produce a circular mark on the photo- 

 graphic paper, and even impress on the latter the lines of an 

 engraving interposed between it and the photographic surface. 



Phosphorescent bodies produce similar effects in a greater degree, 

 and bodies which intercept the phosphorescent effect intercept the 

 invisible radiations. «iA. design drawn by a fluorescent substance, 

 such as a solution of sulphate of quinine on paper, is reproduced, 

 the design being more strongly impressed than the residual parts 

 of the paper. 



Mr. Grove had little doubt that had the discourse been given in 

 the summer instead of mid-winter, he could have literally realised 

 in this theatre the Lagado problem of extracting sunbeams from 

 cucumbers ! 



While fishing in the autumn, 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 tree, gave him the notion that the effect 

 might be photographic, arising from the sunlight having darkened 

 the uncovered, but not the covered portions of the skin. With a 

 fresh fish a serrated leaf was placed on each side, and the fish laid 

 down so that the one side should be exposed, the other sheltered 

 from light : after an hour or so the fish was examined, and a well 

 defined image of the leaf was apparent on the upper or exposed 

 side, but none on the under or sheltered side. There was no 

 opportunity of further experiment ; but there seems little doubt of 

 the effect being photographic, or an oxidation or deoxidation of the 

 tissue determined by light. 



Many important considerations might be suggested as deducible 

 from the above results, as to the influence of light on health, both 

 that of vegetables and animals. The effect of light on the healthy 

 growth of plants is well known ; and it is generally believed that 

 dark rooms, though well heated and ventilated, are more " close " 

 or less healthy than those exposed to light. When we consider the 

 invisible phosphorescence which must radiatC'from the walls and 

 furniture, when we consider the effects of light on animal tissue, 

 and the probable ozonizing or other minute chemical changes in the 

 atmosphere effected by light, it becomes probable that it is far more 

 immediately influential on the health of the animate world than is 

 generally believed. 



The number of substances proved to be molecularly affected by 

 light is so rapidly increasing, that it is by no means unreasonable 

 to suppose that all bodies are in a greater or less degree changed 

 by its impact. 



Passing now to the effects of Electricity, every day brings us 

 fresh evidence of the molecular changes effected by this agent. The 

 electric discharge alters the constitution of many gases across 

 which it is passed ; and it was shown, that by passing it through 



