346 SCIENCE IX SHORT CHAPTERS. 



the space between the doors, and the entry-door is closed ; 

 now the exit-door is opened, and thus no continuous open- 

 ing is ever permitted. 



Only one such opening would derange the ventilation of 

 the whole pit, or of that portion fed by the split thus al- 

 lowed to escape. It would, in fact, correspond to the 

 action of our open fireplaces in rendering effective ventila- 

 tion impossible. 



The following, from the report of the Lords' Committee 

 on Accidents in Coal Mines, 1849, illustrates the magnitude 

 of the ventilation arrangements then at work. In the 

 Hetton Colliery there were two downcast shafts and one 

 upcast, the former about 12 feet and the latter li feet 

 diameter. There were three furnaces at the bottom of the 

 upcast, eacb^about 9 feet wide with about 4 feet length of 

 grate-bars; the depth of the upcast and one downcast 900 

 feet, and of the other downcast 1056 feet. The quantity 

 of air introduced by the action of these furnaces was 

 168,560 cubic feet per minute, at a cost of about eight tons 

 of coal per day. The rate of motion of the air was 1097 

 feet per minute (above 12 miles per hour). This whole 

 current was divided by splitting into 16 currents of about 

 11,000 cubic feet each per minute, having, on an average, 

 a course of 4 miles each. This distance was, however, 

 very irregular the greatest length of course being 9^ 

 miles; total length 70 miles. Thus 168,560 cubic feet of 

 air were driven through these great distances at the rate of 

 12 miles per hour, and at a cost of 8 tons of coal per day. 



All these magnitudes are greatly increased in coal-mines 

 of the present time. As much as 250,000 cubic feet of 

 air per minute are now passed through the shafts of one 

 mine. 



The problem of domestic ventilation as compared with 

 coal-pit ventilation involves an additional requirement, 

 that of warming, but this does not at all increase the diffi- 

 culty, and I even go so far as to believe that cooling in 

 summer may be added to warming in winter by one and 

 the same ventilating arrangement. As I am not a builder, 

 and claim no patent rights, the following must be regarded 

 as a general indication, not as a working specification, of 



