1868. ] Physics. 495 
temperature. M. Deville’s memoir contains tables giving an im- 
mense number of experimental results; it is, however, only a first 
memoir ; more upon the subject will be brought before the Academy 
shortly. It may not be without interest to state that M. Deville 
has undertaken this research by command of the Emperor, to re- 
port upon the most advantageous arrangements to adopt for the 
economic and safe employment of mineral oils, with especial refer- 
ence to its use in transports. 
Exxctrictry.—The fabrication of porous carbon, for electrical 
purposes, engages the attention of no inconsiderable number of 
persons in the present day; this kind of carbon is made most 
advantageously by the following process:—A mixture of wood 
charcoal and animal charcoal is ground to a coarse powder, mixed 
with sawdust, and dried at a steam heat; as soon as the material 
is dried, and while still warm, 20 per cent. of tar is added. When 
cold a certain amount of asphaltum is added, and the mass pressed 
into moulds. The proportions in which the ingredients are used 
vary according to the circumstances. The moulded objects are 
placed in boxes of sheet iron, and covered all over with a mixture 
of sand and charcoal; afterwards they are heated on the sole of -a 
furnace. Gases which are disengaged during the operation are 
burnt in the furnace. The entire operation lasts about 24 hours. 
Careful attention is required during the calcination ; the properties 
of the carbon depend, in a great measure, upon the management of 
this part of the process. 
Some recent correspondence between the Trinity House and the 
Board of Trade shows that the electric light at Dungeness can now 
be worked by either of the two engines, so that no disturbance 
occurs when one requires repair. The services of the high-class 
engineers and firemen have been dispensed with, and the Elder 
Brethren have since been enabled to do that which the connection of 
the men with the trades union prevented—viz. to have their own 
ordinary keepers trained to drive the engines, as well as to attend 
to the lamps, a steady old experienced keeper being placed at the 
head of the establishment. The magneto-electric apparatus shown 
at the Paris Exhibition presented several improvements. The 
working by either of two machines showed that the power or the 
light can be duplicated in thick weather; and the engines were 
utilized for working the pumps of an air fog-trumpet. The electric 
light was compared with the flash of a first-order revolving oil 
apparatus belonging to the French authorities ; and at fifteen miles 
distance the Trinity House engineer, Mr. Douglass, estimated the 
power of the fixed electric light at twice that of the flash of the 
oil light. The superiority of penetrating power of the electric 
light in fog was shaken by some experiments made by the Royal 
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