4 10 Intelligence and Miscellaneous Articles. 



the silver receives an impression of the figure, writing, or crest, which 

 may be cut upon the agate, or horn. The figures, &c, do not ap- 

 pear on the silver at the expiration of the ten minutes, hut are ren- 

 dered visible by exposing the silver plate to vapour, either of amber, 

 water, mercury, or any other fluid. He (Sir D. Brewster) had heard 

 Prof. Bessel say, that the vapours of different fluids were analogous 

 to the different coloured rays of the spectrum ; that the different 

 fluids had different effects, corresponding to those of the spectrum ; 

 and that they could, in consequence of such correspondence, produce 

 a red, blue, or violet colour. The image of the camera obscura might 

 be projected on any surface, — glass, silver, or the smooth leather 

 cover of a book, — without any previous preparation ; and the effects 

 would be the same as those produced on a silver plate covered with 

 iodine. 



This paper gave rise to an animated conversation, in the course of 

 which M. Bessel said that he had seen some of the pictures taken by 

 this process, which were nearly, but not quite, as good as those ob- 

 tained by Mr. Talbot's process. — Sir D. Brewster said, this was the 

 germ of one of the most extraordinary discoveries of modern days ; 

 by it there seemed to be some thermal effect which became fixed in 

 the black substance ; and not only so, but M. Bessel informed him, 

 that different lights seemed to affect different vapours variously, so 

 that there seemed to be something like a power of rendering light 

 latent ; a circumstance which, if it turned out so, would open up 

 very new and curious conceptions of the physical nature of light : 

 on the emission theory, it would be easy to account for this ; on 

 the undulatory theory, he could not conceive how it could be possi- 

 ble. — Prof. MacCullagh said, he believed Newton had somewhere 

 thrown out a suggestion, that luminous particles, as they entered 

 into bodies, might be caught and retained, within certain bounds, by 

 continual attractions. — Sir D. Brewster said, that the experiments 

 which he had performed with nitrous gas seemed to strengthen 

 some such view as this, for, at certain temperatures, we had here 

 an instance of a gaseous body as impervious to light as a piece of 

 iron. — Sir J. Herschel thought it a pity to encumber this new and 

 extensive field of discovery now laid open to them by any specula- 

 tions connected with the theory either of undulations or emissions. 

 He had found that paper could be so prepared, as that the impres- 

 sions of some colours might become permanent upon it, while others 

 were not ; and thus it became possible to impress on it coloured 

 figures by the action of light. He exhibited to the Section a piece 

 of paper so prepared, which, at present, had no form or picture im- 

 pressed on it, but which was so prepared, that, by holding it in a 

 strong light, a red picture would become developed upon it. He 

 wished much he could prevail on Sir W. Hamilton to explain to the 

 Section a metaphysical conception, which he had disclosed to him, 

 and which seemed to him, though darkly he owned, to shadow forth 

 a possible explanation of many difficulties. — Sir W. Hamilton said, 

 that, appealed to by Sir J. Herschel in this manner, he could not 

 avoid placing before the Section the theory alluded to, however im- 



