236 ANNUAL OF SCIENTIFIC DISCOVERY. 



Simple oxymel, glycerine, treacle, and various other substances have also 

 been employed. During this period the somewhat remarkable process of 

 M. Taupenot was published, and was as follows : The plate was first coated 

 with collodion and sensitized in the usual way, the surface washed, and 

 mixture of albumen and honey slightly iodized was poured over it ; it was 

 then allowed to dry, and again plunged into the silver bath and rinsed, when 

 it might be used, either wet or dry. The theory of the process, at the time 

 it came out, was imperfectly understood ; and, as it involved very operose 

 manipulations, it was not so generally used as it deserved. The main point 

 was the coating the excited collodion surface with the albumen, thus filling 

 its pores and preserving it in some measure from the action of the air ; and 

 it being ascertained that even if the whole of the free nitrate were removed 

 by washing, and the plate dried in the dark chamber, it was yet sensitive, 

 although in a inferior degree than when recently prepared. 



Dr. Hill Norris proposed to cover the washed plates with gelatine, and I 

 believe his dried plates preserve their sensibility for many months. 



Mr. Sparling employed a solution of dextrine mixed with honey, and iod- 

 ized in the same way as Taupenot, also following him in two immersions in 

 the silver bath. 



Mr. Maxwell Lyte has yet more recently advocated the use of what he 

 terms meta-gelatine, produced by boiling a solution of gelatine witli sulphuric 

 acid until it ceases to gelatinize on cooling, then removing the acid by diges- 

 tion upon carbonate of lime, fdtering, and adding a portion of clarified 

 honey. This is poured over the plate, without previously washing, and 

 stored away until required for use. This is certainly the quickest, and, as 

 far as I have seen it tried, the most satisfactory process, as it may be used 

 indifferently, either wet or dry. 



SIMPLE METHOD OF DETECTING COUNTERFEIT PHOTOGRAPHIC 



BANK BILLS. 



In most cases, a photographic counterfeit bank note may be detected by 

 the following simple experiment : 



Procure a half ounce of fluid of the solution of Cyanide of potassium 

 which may be procured at any respectable drug store. With a drop or two 

 of this liquid, moisten any part of the suspected bill, and if it be a photo- 

 graph bill the color will in two or three minutes be changed or removed. If 

 the bill be genuine that is, no photograph it will produce no change 

 upon its color or face. 



ON A MOVABLE HORIZONTAL SUN-DIAL. WHICH SHOWS CORRECT 

 SOLAR TIME WITHIN A FRACTION OF A MINUTE. 



In a communication on the above subject, read to the British Association, 

 Dublin, by M. Donovan, the author first gave a short account of common 

 horizontal dials, showing that, in consequence of the penumbral shadow of 

 the gnomon, they could scarcely ever give the time within three minutes, 

 even when they were well constructed and carefully set. He then explained 



