138 Notices respecting New Books. 
give unexampled extent and perfection to this apparatus: the 
insulated wire has been extended to the extraordinary length of 
one mile and a quarter ; and a variety of ingenious contrivances 
have been applied to preserve the insulation. But the length of 
the wire rendered it so liable to injury, and subject to depreda- 
tion, that it has been found expedient to shorten it to 1800 
feet, aud until the present time no means have been devised 
that sufficiently preserve the insulation during a dense fog, or 
driving snow.”’ 
The apparatus has been preserved in constant activity during 
eighteen months; and a series of observations have been made 
with it, which afford some very interesting information on the 
subject of atmospherical electricity. The details which Mr. 
Singer has given are, however, too extensive for the limits of 
this notice ; and we must refer the reader to the work itself for 
the information they contain. 
In pursuing these inquiries, Mr. Singer has been led to a dis- 
covery of the first importance to the practical electrician. It is 
well known that one of the most perplexing cares attendant on 
electrical experiments, is the preservation of the insulating parts 
of the apparatus in a perfectly dry state; and in moist weather 
this is so far from practicable, that many experiments are from 
necessity avoided in consequence. Mr. Singer has contrived 
an arrangement which prevents the free contact of the air 
with the surface of the msulator, and consequently precludes 
the deposition of moisture upon it, and preserves it In a proper 
state for use under nearly every variation of weather. The — 
gold-leaf electrometer constructed on this principle becomes 
a truly valuable instrument: it retains its electricity for a con- 
siderable period ; and as it scarcely ever requires to be warmed © 
or wiped, is much more useful, and less liable to be deranged, ~ 
than in the old construction. The deseription which is given of ~ 
this method of insulation is nearly confined to the development 
of its general principle, and is by no means so extensive as we 
could have wished; for we deem it one of the most useful dis- 
coveries in practical electricity which has come under our notice 
for some time. 
The experiments of Nollet and others on the action of elec- 
tricity on organized bodies are mentioned as introductory to the 
practice of medical electricity, which is developed with much 
skill within very moderate limits : an account of the torpedo and 
gymnotus, which comprises the most interesting facts that are 
at present known concerning those animals, precedes a detail of 
the experiments of Galvani, Volta, and others, to the period at 
which the latter produced his extraordinary invention of the 
Voltaic battery. This part of the subject is not extensive, but it 
appears 
