COAL MINING. 369 
The plan of splitting the air is not followed to any extent in the 
mines of this State. The pits are so shallow that it costs less to sink 
a new air-shaft at the interior of the workings than to provide any 
elaborate system of ventilation. — | 
The manner of measuring the current of air circulating in mines is 
simple and speedy. . Biram’s and Castello’s anemometers are the instru- 
ments in general use. Biram’s 4-inch instrument reading to 100 feet is 
largely used by mining bosses. The anemometer self-registers the speed 
of the current. The vanes are so constructed that they revolve by the 
current of air impinging upon them. A point is selected in the air- 
course where the whole column of air passes ; the instrument is held up 
in the current, and its speed is indicated by the rotary motion of the 
index hand or pointer of the dial-plate, which reads to single feet. 
One revolution of the pointer records 100 feet. The instrument is 
usually held in the air-way a single minute; it indicates, say 340 feet 
per minute, and the air-way is 65 feet high and 9 feet wide; the quantity 
of air in circulation per minute is found by multiplying the speed of 
the current by the sectional area of the air-way, which in this case 
would be 19,890 cubic feet of air per minute—the sectional area of the 
air-course being 583 feet, which, multiplied by 340, gives the above 
result. This is a current strong enough, if properly distributed, to ven- 
tilate any mine in the State. 
In taking measurements with the anemometer, an allowance has to 
be made for the friction of the instrument, which is equal to 17 feet 
per 50 feet, 8 feet per 100 feet, 4 feet per 200 feet, 3 feet per 300 feet, 2 
feet per 400 feet. ‘The speed of currents varies from 100 to 400 feet 
per minute in mines, according to the ventilating power in use. A 
current exceeding 400 feet per minute in speed is not desirable ; it blows 
out the miner’s lamp, and chills his body. Currents of this speed are 
only found along the main air-courses of the mine. The complaints 
which arise trom too strong currents of air are like angels’ visits, few 
and far between. 
Castello’s anemometer or air-meter is made on the same principle 
as Biram’s. It is smaller and more easily injured. Some of these air- 
meters have a minute sand-glass attached, which is a great convenience 
in taking accurate measurements. 
24 Gr 
