415 



sixty miles at the rate of tliree miles per hour, it will be 

 twenty hours before it can escape at the upcast pit. But 

 if the same be split into six currents, each will only travel 

 ten miles, and at the same rate will be detained in the 

 mine little more than three hours. Besides, so conducted, 

 a general explosion is impossible. 



4. The dangerous nature of the ditferent goafs in a mine, 

 requires much greater caution than is usually given respecting 

 them. Their boundaries may vary from — 



1. Atmospheric, or barometrical changes. 



2. Falls of the ground, or extensive ground weights, 



as called. 



3. From irruptions of gas out of a superior seam of 



coal, however thin. 



4. From a gradual rising of the gas towards the upper 



and more elevated portions of the mine. 



One side of the goaf must necessarily be open, and it is 

 requisite, therefore, that an active ventilation be enforced 

 against or adjoining those portions which are exposed to- 

 wards the works, and in the next place, that periodically, 

 the precise boundary of the inflammable air be remarked 

 and registered, A very simple way of examining the air 

 in goafs, is by having a bottle of the capacity of three or 

 four quarts, made of tin, and having two corks or stop- 

 cocks, filling it with water and emptying it in the goaf, 

 and recorking it at the same place. The vessel will then be 

 filled with air ; and if taken to a safe part of the works, may 

 be examined by passing the air through a glass tube to a 

 candle, as, for instance, the chimney of an argand lamp.* 



♦ Professor Graham proposes an instrument to be used which will measure the 

 velocity with which gas passes into a vacuum, this velocity being equal to the 

 square root of the density of the gas. Hence the exact amount of fire-damp in 

 any place could be ascertained. — See Report of British Association for 1845, 

 p. 28. 



