CHEMICAL SCIENCE. 195 



through the roof of the theatre. He immediately procured a lumi- 

 nous pencil from the bead projecting a bright spot of light, denoting 

 about 45° of vitreous electricity ; upon which he observed that he 

 was happy to state, for the information of those who were interested 

 in the fact, that the rain had ceased, that there woiftd be a fine 

 evening, and a succession of very fine days. "From that mo- 

 ment, oti that Friday evening, until the following Saturday week, 

 we had not one drop of rain (says the writer) in London." 



For military purposes, again, Photography has proved exceedingly 

 useful. Captain Fowke, of the Royal Engineers, who has fitted out 

 most of the parties of engineers that have taken photographic appa- 

 ratus with them, invented a form of camera which is extremely port- 

 able, collapsing into a size that enabled it to be easily carried in a 

 knapsack. The back of the camera is three or four times the size of 

 the front. The sides can be detached from the front, but are hinged 

 to the back in such a way as to allow them to fold one upon another 

 flat upon the back. With a camera of this description, and with 

 chemicals, &c, carried in boxes on pack-saddles, many photographs, 

 which Captain Donelly exhibited, have been taken by sappers in 

 Russia and Turkey ; and pictures by Sergeant Church, who accom- 

 panied Colonel Stanton when he went to verify the reports on the 

 projected Honduras line of railway across the Isthmus of Panama. 

 Others were done in India and at Singapore. Some were taken in 

 China, and furnished Mr. Burford with the means for his Pano- 

 rama. Others were taken by Sergeant Mack at Moscow, when he 

 accompanied Lord Granville. 



Photographs are found of great service in illustrating a report on 

 a country, as they have been employed by Colonel Stanton ; and in 

 this way they may be of service to a general commanding an army 

 in the field. Photographs are also available in copying and multi- 

 plying plans, — as in the case of a plan, which was produced, of the 

 position of the ships for landing the troops in the Crimea. Captain 

 Donelly iustances a number of photographs which were executed 

 at Chatham, affording an admirable means of conveying descriptions 

 of various operations (bridge-making and so on), giving perfect ideas 

 of place. Photographs are likewise of great service in supplying 

 engineers with a ready and rapid means of showing the state of works 

 on a particular day. 



PHOTO-ZINCOGRAPHY. BY COLONEL SIR HENRY JAMES, E.E., DIRECTOR 

 . OP THE ORDNANCE SURVEY. 



In the Fieport of the Committee of which Sir P. Murchison was 

 chairman, it is stated that the annual saving effected by my having 

 introduced this (the photographic) method of reducing the Ordnance 

 plans from the larger to the smaller scales, amounted in the year 

 1858 to \G15l. Since then we have so much reduced the cost of the 

 photographs, that the saving which will be effected will amount to 

 25,0001. in the cost of the survey. Up to this period we have ex- 

 clusively used the paper prepared with nitrate of silver for printing 

 the number of copies required j but we have made experiments with 



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