298 SCIENTIFIC APPARATUS. 



experiments and report of a committee appointed by the Northern 

 Institute of Engineers. Some of them have been devised with 

 special reference to further impeding the passage of flame, and 

 have been stated to resist the effect of a current flowing with a 

 velocity as great as forty or fifty feet per second. 



Sundry modes of lighting the workings by electricity have from 

 time to time been proposed ; but although particular spots occur 

 where something of the kind may be useful, as, perhaps, in a South 

 Staffordshire thick coal working, it may be asserted, with all 

 deference to the ingenuity of the projectors, that such a method 

 of lighting is as a rule inapplicable to extensive collieries. 



METEOROLOGY OF MINES. 



Underground observations of temperature and barometric 

 pressure have in many cases been carried out from purely abstract 

 scientific motives, but they now form in a great number of our larger 

 collieries an item in the regular daily work with reference to the 

 ventilation, upon which the health and safety of the men depends. 

 For this latter purpose a strong and simple mercurial barometer 

 is ordinarily placed in a cabin or room near the pit-bottom, sure 

 to be often visited by the overman, or sometimes nearly adjoining 

 the ventilating furnace. In the latter position Mr. J. T. Woodhouse 

 commenced above a quarter of a century ago to make it a sine 

 qua non, and substituted for the common legend Fair, Rain y 

 Stormy, the hints to the furnace-men, Fire slow, Fire moderate 

 Fire heavy. 



Several observant persons have at intervals pointed out the 

 connection between the weather and the condition of the air in 

 mines, and there can be no doubt about some few deductions of 

 deep moment, viz., that the evolution of gas from the face of the 

 workings, as also from blowers, is greater when the atmospheric 

 pressure is less ; that when surface temperature increases, the ven- 

 tilating current becomes more sluggish ; and that when, as occurs 

 so commonly, the two changes of depression of barometer and 



