70 



DuBois.] • ^ [April 5, 



"We cannot claim for the thinnest of these films that they represent 

 a single layer of molecules. Taking Sir William Thomson's estimate of 

 the size of the final molecules, and considering that each laj'er corre- 

 sponds to one page of a book, our thinnest film would then make a pam- 

 phlet having more than a hundred pages. It is found that when such a 

 film is interposed between the eye and any object it is as transparent as a 

 piece of glass. Tliis may be readily proved by projecting a picture on 

 the screen and interposing the leaf of gold in the path of the light and you 

 see that the only apparent effect is to tinge the light a pale greenish color, 

 none of the detail of the picture is lost, though all the light is coming 

 through a piece of gold as absolutely continuous in its structure, when 

 examined under a microscope, as though it were an inch thick. By plac- 

 ing in the lantern a piece of ordinary gold leaf, having a thickness of 

 about 2tfirVot» ^f ^^ inch, and a piece of electro-plated gold leaf about 

 sTo^oSTiJou <^f ^^ ^'^•^'^ thick, mounted side by side on a glass slide and 

 focusing their images on the screen, you will see a very great difference in 

 the amount of light transmitted by the two, owing to the difference of 

 thickness." 



One particularly interesting thing about the foregoing extract is that 

 the lecture from which it was taken was bound in as a part of the litera- 

 ture relating to the exhibition, and sent broadcast to exhibitors and others, 

 to whom Mr. Swan's revelations ought therefore to come with no degree 

 of novelty. 



The Journal of the Franklin Institute, in its issue of September, 1894 

 (Vol. cxxxviii, 825), refers to the Outerbridge and Swan processes in an 

 article which concludes as follows: 



"It may be stated, in conclusion, that the mode of procedure above 

 described was patented by its author [Alexander E. Outerbridge, Jr. ], 

 under the title 'Manufacture of Metallic Leaf In his patent the inven- 

 tor describes, as 'a new and improved method of manufacturing gold leaf, 

 silver leaf, and other metallic leaf,' the above-named method of electrical 

 deposition. As suitable mediums to support his films, he mentions copper 

 in thin sheets, and paper, shellac, wax, etc., made conductive upon the 

 surface which is to receive the deposit. 



"For removing the deposited film from copper and paper, Mr. Outer- 

 bridge describes the use of a bath of dilute nitric acid, or of perchioride 

 of iron. In the case of the shellac, wax, etc., alcohol, benzine and other 

 solvents are referred to." 



The patent granted to Mr. Outerbridge is No. 193,209, and is dated 

 December 18, 1877. 



The American Philosophical Society is presumably interested in ques- 

 tions of scientific priority, especially when that priority is American, and 

 still further, when it is Philadelphian. As Mr. Outerbridge and I worked 

 side by side for twelve years as assistants in the Assay department of the 

 Mint in this city, I am glad to add my testimony towards the substantia- 

 tion, if such were necessary, of the facts herein mentioned. As stated 



