REVIEWS. 
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capricious command of Pietro de Medici, was at one time compelled to mould 
a statue in snow. Art in perishable material is always a thing to sigh over, 
and even if a photograph he not in every sense a work of art, it is never- 
theless painful to see the beautiful sun-pictures slowly fade away. Per- 
manence is what the photographer long struggled after, and what he at last 
secured by the carbon process. Of all the chemical elements carbon is 
perhaps the most stable j and the ink with which these lines are printed, 
having carbon for its basis, is well-nigh imperishable. Various processes 
have been introduced to the photographer for printing his pictures in media 
containing carbon, the germ of these processes being found in the remarkable 
effect of solar light on bichromate of potash in solution of gelatine. All the 
practical details of carbon-printing are clearly given by Dr. Liesegang in 
the neat little work before us, which forms one of the 11 Bibliothek fur 
Photographen.” We find, of course, a description of the author’s method 
of producing enlarged carbon prints from small negatives. The work also 
contains much information on the production of permanent photographs for 
the magic lantern from small objects viewed under the microscope. So 
much attention is now paid in Germany to the magic-lantern as a means of 
scientific instruction, that a journal entitled the 11 Laterna Magica,” edited 
by Dr. Liesegang, is now regularly issued at Diisseldorf. 
Dr. Tyndall's Electricity * — To administer doses of science to juveniles 
home for their Christmas holidays is a task more difficult and delicate than 
some people may be willing to concede. Dr. Tyndall, however, is singu- 
larly successful in this work, and always contrives with rare tact to gild the 
scientific pill. The lectures on electricity in the work before us are admir- 
able examples of the way in which experimental science may be effectively 
presented to boys and girls. All the experiments are ingeniously devised 
and inexpensively carried out. In fact the special feature of the work con- 
sists in showing how the leading principles of statical electricity may be 
demonstrated with simple apparatus of very homely type. Apples, potatoes, 
eggs, straws, tin-foil, glass tumblers — such are the familiar objects with 
which the greater number of the experiments are performed. It is often 
objected that physical science cannot be taught in schools in consequence of 
the expense of apparatus. Whilst admitting that there is something in this 
objection, it certainly loses half its force on a perusal of these lectures. In- 
deed, almost everything used in the experiments here described may be had 
for a five-pound note. And surely no school could object to so small an 
outlay for a course of lectures on electricity. 
* “ Lessons in Electricity at the Loyal Institution, 1875-6.” By John 
Tyndall, LL.D., D.C.L., F.L.S. London : Longmans. 1876. 
