608 KANSAS CITY REVIEW OF SCIENCE. 
strong wood the concentric rings appear close in texture, while the radial plates 
are numerous, broad, and thick. It has even been suggested that such photos 
migh be used as trade advertisements. The internal structure of metals, too, has 
been examined by the joint aid of the camera and microscope ; laminae of the 
metals are reduced to extreme tenuity by the action of acids, and when suffi- 
ciently translucent are photographed through the microscope; gold and silver are 
said to have a fibrous structure, while tin is granular. 
Till recently, no one would ever have dreamed of applying photography to 
acoustics ; but it is now possible to photograph sound, or, speaking more accurately, 
sound-vibrations; and Professor Boltzmann is now announced as the discoverer 
of what at first might well be regarded with incredulity. The sound-vibrations 
are communicated to a thin platinum plate, and the movements of the plate, after 
being magnified by a solar microscope, are reflected on a screen and photo- 
graphed by rapidly drawing a sensitive plate across the image. Every letter 
when pronounced gives a separate and distinct impression, the vowels showing 
regular undulatory vibrations, while the consonants give curves and lines of very 
varied forms. The uses of an arrangement like this may be innumerable. We 
can almost imagine that when the process is perfected, eavesdroppers and spies 
will have a very easy time, and need to run no risks in order to obtain secret 
information ; a small instrument secretly placed in a room, and acting automati- 
cally, may copy down every word spoken ; nay, it is far more chimerical to 
expect that photography may one day take the place of short-hand reporters. 
But besides all the varied ways in which photography has been utilized in 
science, it has miscellaneous uses without number, and especially noticeable are 
the ways in which the British and foreign governments have found it serviceable. 
No army is now ever despatched on service without a full equipment of photo- 
graphic requisites. In reconnoitering and surveying the enemy's positions and 
intrenchments, it was formerly necessary to have sketches made; considerable 
time was needed, many dangers incurred, and after all, important details were 
often accidentally omitted. Now the photographer accompanies the reconnoi- 
tering party, and in a second or two he secures views which show the exact 
positions of the enemy's works, without a chance of mistake. Such photos were 
found of great use in the recent war in Egypt. 
Again, during the last siege of Paris, it is well known of what enormous 
value the pigeon post was. The beleaguered Parisians were able to keep up 
correspondence with their friends outside, in spite of the German army. Letters 
and despatches were printed on a large sheet which was then photographed to a 
very small scale on pellicles of six by two centimetres in dimensions; and these, 
being tied to the legs of trained pigeons, were carried over the heads of the Ger- 
mans safely to their destination. The small photos had then only to be placed 
in an enlarging lantern, the letters transscribed and sent to the various addresses. 
The Germans have now established a regular system of pigeon-post in all their 
large towns, in the event of war. 
