136 ANNUAL OF SCIENTIFIC DISCOVERT. 



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. The number of substances proved to be molc- 

 cularly affected by light is so rapidly increasing, that it is by no means un- 

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

 by its impact. Passing now to the molecular 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 an attenuated atmos- 

 phere of the vapors of phosphorus, this element is changed by the electric 

 discharge into its allotropic variety, which is deposited in notable quantity on 

 the sides of the receiver. In this experiment, the transverse bands or striae 

 discovered by Mr. Grove, in 1832, are very strikingly shown. The glow which 

 is seen on excited electrics, such as glass, was also shown by Mr. Grove to be 

 accompanied with molecular change. Letters cut in paper, and placed be- 

 tween two well-cleaned sheets of glass, then formed into a Leyden apparatus, 

 by sheets of tin-foil on their outer surfaces, and then electrified, by connec- 

 tion for a few seconds with a Ruhmkorf coil, had invisible images of the let- 

 ters impressed upon the interior surface, which were rendered visible by breath- 

 ing on them, and rendered visible, and at the same time permanently etched 

 by exposure, after electrization, to the vapor of hydrofluoric acid. So, again, 

 if iodized collodion be poured over the surface of glass having the invisible 

 image, and then treated as for a photograph, and exposed to uniform day- 

 light, the invisible image is developed in the collodion film, the invisible 

 molecular change being conveyed to the molecular film, and rendering it, 

 when nitrated, more sensitive to light in the parts where it has been in pi-ox- 

 imity to the electrical impression, than in the residual parts. Here we have 

 a molecular change, produced first by electricity on the glass, then commu- 

 nicated by the glass to the collodion, then changed in character by light, and 

 all this time invisible, and then rendered visible by the developing chemical 

 agent. Mr. Babbage had observed that some plates of glass which had 

 formed the ornamented margin of an old looking-glass, and were backed by 

 a design in gold-leaf covered with plaster of Paris, showed, when this back- 

 ing was removed by soft soap, an impression of the gold-leaf device, which 

 was rendered visible by the breath on the glass. Some of the plates had 

 been kindly lent by him for this evening; and in one, Mr. Grove had removed 

 a portion of the backing, and the continuation of the gilded design came 

 beautifully out by breathing on the glass while in the frame of the electric 

 lamp, and was projected (as were the previous electrical images) on a white 

 screen. Of the practical results to science of the molecular changes form- 

 ing the subject of this evening's lecture, a beautiful illustration was afforded 

 by the photographs of the moon by Mr. De la Rue, which afforded, by the 

 aid of the electric lamp, images of the moon, of six feet diameter, in which 

 the details of the moon's surface were well defined, the cone in Tycho, the 

 double cone in Copernicus, and even the ridge of Aristarchus, could be 

 detected. The bright lines, radiating from the mountains, were clear and 

 distinct. A photograph of the planet Jupiter was also shown, in which the 

 belts wei^e very well marked, and the satellites visible. The following question 



