SCIENTIFIC SUMMARY. 129 
atmosphere, the various substances examined by him became impregnated 
with it.” — Vide Philosophical Magazine , November. 
Pressure and Temperature of the Air in Mines. — M. Simonin’s experiments 
do not enable him to establish any general laws, but the mean of four experi- 
ments at the coal-mines of Creuzot and Epinac gave a rise of one degree (C.) 
of temperature for every 45 metres of vertical descent, and a rise of one 
millimetre in the barometer for every 10^ metres of vertical descent. — Vide 
Comptes Rendus, Dec. 4. 
A new Insulating Material. — Mr. W. A. Marshall, Leadenhall-street, 
London, has invented an isulating material for telegraphic and other pur- 
poses. It consists in the employment of asbestos or amiantus (amiante) for 
insulating purposes. The invention also consists in protecting and com- 
pleting the insulation of telegraphic wire, especially for submarine and 
subterranean purposes, previously covered with the asbestos or amiantus by 
surrounding or inclosing it in a metal tube, by preference of tin. 
Simple Form of Filter. — A very simple and perfect form of filter has been 
devised by the Apparateur of the College of France, and deserves attention. 
It is made by placing in a tank of impure water a vessel so arranged that a 
sponge which it contains shall lap over its edge and dip into the water of the 
tank. The sponge gradually sucks up and purifies the water in the reservoir, 
and allows it to drop into the smaller vessel or receiver, from which it may 
be drawn off by a tube. By placing a few lumps of charcoal in the bottom of 
the receiver, filtration of the most perfect kind may be effected. 
Electricity in Sounding. — A very ingenious instrument for obtaining the 
accurate soundings of deep water has been devised by M. Hedouin, of 
Lyons. The difficulty which presents itself in the case of the apparatus at 
present employed is to ascertain the exact moment at which the lead touches 
the bottom. This obstacle is removed by M. Hedouin’s invention. In his 
contrivance the sounding-line is a kind of light telegraph cable inclosing two 
perfectly insulated wires, both connected at one extremity with the lead, and 
at the other with the two poles of a galvanic battery. The lead is so arranged 
that on touching the bottom, contact is made between the ends of the two 
wires ; thus a current is established, and this, by ringing a bell placed in 
connection with the battery, announces the exact moment at which the lead 
touches the sea-bottom. 
Spectrum Analysis in the Detection of Chlorine , Iodine, &c. — The difficulty 
of recognizing small amounts of iodine, bromine, and chlorine in a mixture of 
haloid salts is well known. Hitherto it has been found impossible to detect 
these elements in such mixtures, when exceedingly small quantities were 
present. Herr Mitscherlich has, however, discovered a method of detecting 
them by the spectroscope, and he gives it in a late number of Poggendorffs 
Annalen. It is as follows : — The substance to be examined, well dried, is 
intimately mixed with half its weight of sulphate of ammonia and one-tenth 
its weight of oxide of copper. This mixture is placed in a globular enlarge- 
ment of a combustion-tube, one end of which is connected with a hydrogen 
gasometer, the opposite end being open. A stream of hydrogen is passed 
through the tube, and heat graduallly applied to the mixture. The hydrogen 
being ignited, the first appearance seen in the spectrum apparatus is a bright- 
ness in the green, in which, however, no definite spectrum can be perceived ; 
YOL. V. NO. XVIII. K 
