CHAP, vji.] PHOTOGRAPHY ON PAPER AND ON GLASS. 311 



Ill medicine, in physiology, this branch of photographic art has 

 rendered valuable services. Dr. Ozanani has designed an apparatus 

 which registers, photographically, the beats of the pulse in every phase ; 

 he obtains thus an undulating line, which, when magnified, shows all 

 the variations which are produced in the pulsation during the short 

 interval of the hundred-thousandth part of a second. 



To sum up, the innumerable forms discovered by the microscope in 

 the domain of natural science, are permanently placed before us by 

 photomicography, and, by enlarging the 

 proofs, we are enabled to study them at 

 leisure arid with ease. 



During the siege of Paris, this applica- 

 tion of photography rendered service of a dif- 

 ferent kind. It enabled the longest and most 

 voluminous despatches to be reduced to- a 

 surface of a few square centimetres, and to 

 be conveyed under the wings of carrier- 

 pigeons from the provinces to Paris. The 

 organization of this microscopic post was 

 commenced at Tours under the direction of 



a photographer of that town, a M, Blaize, \mSu- ^^^^-^^.^^^^ 

 The reduced proofs were first made on paper ; Fro . 2-2-2. -Microscopic photograph 



,. . . , , Facsimile of a despatch sent to 



two pages oi print were condensed on each Pam during the siege. 

 side of the sheet ; but the grain in the 



paper limited the fineness of the text, and besides, the time for 

 exposing it (in winter) w r as considerable. Hence the system which 

 M. Dagron, who was sent from Paris to Tours by balloon, pro- 

 posed to the Delegation, was preferred (end of November 1870). 

 This photographer operated on thin pellicles of collodion, very light 

 and sufficiently sensitive to need only two seconds exposure instead 

 of two hours. He thus describes his method : 



" Each pellicle was the reproduction of twelve to sixteen pages in 

 folio of print, containing on an average, according to the type, three 

 thousand despatches weighing together less than half a gramme. The 

 whole series of official and private despatches made during the siege of 

 Paris, numbering about one hundred and fifteen thousand, weighed 

 one gramme. One single pigeon eould have easily carried them. If 

 one multiplies the number of despatches by the number of copies 



