11G SCIENTIFIC NOTES. 



nience, and is not more trouble than that required for an ordinary 

 wet plate. No more silver baths need then be used to wash out 

 the operator's patience. The process of making the pellicle is of 

 course a secret, but Mr. Kennett told me that he had succeeded in 

 making it so sensitive by removing from the pellicle all the salts 

 formed in the transfer from the neutral to the sensitive state. It 

 has long been known that these salts acted upon the silver dep< tsited 

 by the light, and the sensitiveness of a plate was much increased 

 by exposing it to a weak light before it went into the camera, 

 which produced a light deposit of silver, and in part satisfied the 

 solvent properties of these salts ; but no convenient way of remov- 

 ing them was known till now. One curious difficulty met Mr, 

 Kennett. Though ordinarily he had no difficulty in making the 

 pellicle adhere to the plate, yet at times it would peel off every plate 

 coated. Without recounting his experiments in tracing the cause 

 of this, it is enough to say that it was at last found in the 

 state of the atmosphere. If much ozone is present, a slight acidity 

 is produced in the pellicle, and it will not adhere ; but the addition 

 of a little soda cures it at once. In Germany another old idea has 

 found some one to work it out to a practical result ; and now a 

 picture perfectly sharp and clear all over, and covering an angle of 

 1 1 3°, is taken on a long flat plate, the camera being kept in motion 

 while the glass plate is passed along a slide at the back of it, so 

 that as the camera takes in new points of view, new parts of the 

 sensitive plate are brought forward to receive the picture. 



Of the application of photography to facilitate printing, there 

 are several beautiful processes, not new, but only now coming 

 into general use for ordinary illustration. There can I think be no 

 doubt that the Woodbury type produces the most perfect pictures ; 

 indeed they are so like the finest silver prints that I doubt if one 

 could be told from the other. The process is wonderfully cheap, 

 even in the hands of the London Company, who have the 

 monojDoly ; and it is said one man can print without assistance 

 100 copies per hour of the ordinary carte-de-visite. 100 copies 

 may be had for 10s. One difficulty, however, stands in the way 

 of this process, the enormous pressure required to make the lead 

 printing block. On plates 12 x 15, a pressure of 400 tons is 

 required. The Albert type process is also much used in England 

 and America, but the inventor is in the happy position of Court 

 Photographer generally in Europe, and does not trouble himself 

 about such a small matter as the printing process. The heliotype 

 is, like the Woodbury type, an English invention, but the process 

 and the inventor have been bought by the large publishing house 

 of Osgood & Co., Boston. 



Of the heliotype process there are several modifications ; thus, 

 if' 500 copies are wanted, they are printed from a gelatine 

 surface ; if a greater number, up to 2,000, then stone is used • 



