NATURAL PHILOSOPHY. 185 



authorities themselves as well as the public, for it is possible to pro- 

 duce, by these means, imitations, which not the most skilful teller 

 or the most practised expert could detect or make oath as to the 

 forgery. 



Let us take the case of photo-zincography, photo-lithography, or 

 the processes which have at present attained the highest state of per- 

 fection. The results of these processes, in the shape of facsimiles of 

 maps, engravings, manuscripts, pages of printed books, etc., were ex- 

 hibited at the International Exhibition, in a shape to absolutely defy 

 detection as copies. But it is said that the inventors of these new 

 processes are gentlemen from whom there is no danger of forgery. 

 But their processes are made public, and not only may be, but 

 actually are, practised by others. In fact, Mr. Osborne, the inventor 

 of photo-lithography, wishing to call the attention of bankers in Mel- 

 bourne to this danger, produced to them photo-lithographic copies of 

 which they admitted they would be unable to repudiate the genuine- 

 ness. Any color of ink, resembling either printing or writing ink, or 

 any number of colors, may, of course, be easily produced, so that an 

 actually written signature, instead of the printed signature now used, 

 would not be an absolute safeguard. 



We do not enter at present into any extended examination of the 

 means by which such forgeries might be prevented, our object being 

 rather to call the attention of those concerned to the existence and 

 imminence of the danger. The means of prevention require careful 

 consideration, and are not so easy and simple as might at first sight 

 appear. Some years ago the subject came under consideration in the 

 United States and in Canada. Colored inks were employed for some 

 parts of the note, and black for the other ; but it was found that the 

 colered inks, not possessing, like black, a carbon basis, were easily dis- 

 charged by chemical means, and photographic copies of the remainder 

 easily produced, the colored portion being supplied by a subsequent 

 operation. This difficulty was subsequently met by the use of a green 

 formed of the oxide of chromium, which resisted the action of chem- 

 ical reagents. A geometrical pattern in this color was printed first 

 all over the paper, and the value, denomination, etc., of the note, sub- 

 sequently printed upon that in the usual way with black ink. This 

 was an effectual check to ordinary photographic imitation, but it 

 would be little or no check to the photo-lithographer, whose art would 

 furnish him with means of evading this difficulty. A variety of means 

 might be suggested of making the imitation difficult, but they would 

 require more consideration than we can now give to the subject. 



NEW METHOD OF MAP CONSTRUCTION. 



At a recent meeting of the Franklin Institute, Mr. Sartain, the well- 

 known engraver, exhibited a map, devised and executed on a new 

 plan, by Baron Egloffstein, for illustrating the labors of the United 

 States expedition for exploring the Colorado River of the West. 



Baron Egloffstem, the topographer of the expedition, conceived 



the idea of endeavoring to give his map the appearance of a small 



plaster model of the country ; and to do this he treats the forms of 



nature as an artist would draw any form before him, that is, by 



16* 



