128 ANNUAL OF SCIENTIFIC DISCOVERY. 



•* I generally ap])ly the solution Avarm with a flat camers-hair 

 brush, crossinfi: it till it lies evenly. "When the i)aper is dry it is 

 ready for scnsitizinix, which may be done either by llotatioii on 

 the ordint4ry printinLT-bath, or by brushing on the silver solution. 

 I prefer to use the ammonia-nitrate sohition brushed on; but there 

 are specimens by both methods betbre you. I use 40 grains of 

 silver to the ounce of water. Some of the ammonia-nitrate prints 

 contain also a large jn'oportion of citrate of silver in addition to 

 the usual ammonia-nitrate. 



**As you will see, the tones of many of the untoned prints are 

 quite as line in color as arc those toned with gold, and 1 attribute 

 this entirely to the variations in the salting and in the strength of 

 the size and lac S(dution, and to the minute variation of the silver 

 bath by the addition of various salts in the course of sensitizing. 



THE ALBERTYPE. 



A recent number of the London '* Photographic News " contains 

 a fine example of this new style of i)liotograpliic pictures. The 

 process is as follows : A plate of glass is covered with a solution 

 of albumen, gelatine, and i)ichromate of potash, dried and ex- 

 posed to light until hardened. It is then again covered with a 

 solution of gelatine and bichrcmiate of potasJi, and when dry ex- 

 posed under the negative, and the film is then found to possess 

 (jualities analogous to a drawing made with fatty ink upon litho- 

 graph stone. All those portions of the film that were acted upon 

 by the light will refuse water and take printing-ink, while those 

 portions which were protected from light Ijy the negative will 

 take water and refuse ink. The ink and water will be absorbed 

 by the film just in accordance with the gradations of light and 

 shade in the negative. To produce a picture, wet the surface of 

 the film, then apply ink, lay on paper, and pass through a press; 

 the operation being stibstantially the same as lithography. The 

 process is said to be rapid, and excellent pictures of all sizes may 

 be printed in admirable style. 



SUMMARY OF IMPROVEMENTS IN THE MECHANIC ARTS, ETC. 



Photocjrapliing a Tunnel. — We have latel}' seen a ])hotograph, 

 taken by sunlight, of the interior of the tunned which j^onetrates 

 the summit of the Nevada for the distance of l,Go9 feet, at an ele- 

 vation of 7,042 feet above the sea level, the greatest height to 

 which a locomotive has yet attained. The success of this picture 

 is due to the position of this tunned, through which, liice that near 

 Bore, on the Great Western llailwa}', the sun shines for a few 

 days each year. Taking advantage of this circumstance, and 

 also using mirrors by which light was thrown successively upcni 

 various points, this picture was produced with an exposure of 15 

 minutes, and shows the distant heading with perfect distinctness, 



