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POPULAR SCIENCE REVIEW. 
from the coal. This is effected by having two shafts, and by 
placing at one of them, which forms the upcast, either one or 
more furnaces in the different coal seams worked, or a revolving 
fan at the top of the shaft, which extracts the air in the 
workings. 
Forty years ago no mechanical means were in use for measur- 
ing the velocity of currents of air passing through a mine, the 
rate being then ascertained by carrying a lighted candle exactly 
at the same rate as the current, so as not to deflect the flame, 
which method is accurate up to velocities of 400 feet per minute, 
but is not applicable to the principal splits of large collieries 
of the present day, in which the speed of the current would re- 
quire a person to run. Another method that is still used for 
measuring its velocity is watching the time gunpowder smoke 
takes to travel over a given measured distance, of which the sec- 
tional area is known. 
The first anemometer was invented by Mr. Thomas Elliott (a 
brother to the present baronet. Sir George), in 1835, and was 
worked by “ the air acting on four wands, similar to a windmill, 
which met so strongly with the approval of the coal-owners ” 
that they presented him with ten guineas ; but they did not 
adopt it in one of their mines. 
Anemometers that have since been constructed belong to three 
classes : — 
(a.) Vanes revolving by impingement of the current of air, 
registering rate by a pointer, as Combe’s, 1837 ; Biram’s, 1842 ; 
Whewel’s, Osier’s, and Bobinson’s. 
(6.) Instruments not revolving, but affected by the force or im- 
pulse of the wind, as Dr. Lind’s, Henaut’s, Bougier’s, and 
Dickenson’s. The latter consists of a light, counterpoised, flat 
fan plate, usually made of talc, being on two fine bearings. The 
plate moves up an arc, graduated in feet, which gives the velocity 
per minute, which, multiplied by the area, gives the cubic 
quantity. 
(c.) Those of a more complete character, as Leslie’s, in which 
the velocity is deduced from differences of temperature. 
An ingenious application of the telephone, to test the state of 
the ventilation of a mine without a descent being made, was 
tried last year on the Wigan and Whiston Collieries, by Mr. 
Hall, H.M. Inspector of Mines, in the presence of Sir William 
Thompson. One of Biram’s anemometers, generally used in 
collieries to detect the velocity of the air, was attached to a 
telephone, in which a small thin iron box was substituted for 
the ordinary diaphragm, which vibrated at every tenth revolu- 
tion of the anemometer ; this was taken down the shaft and main 
intake and connected with a telephone in the office on the 
surface, by 600 yards of ordinary coated electric wire. The 
