AND FROM SOME LONDON LAW COURTS. 185 



if it has time to cool, from the height and space being 

 great, the carbonic acid may be arrested before reaching a 

 great height. 



If from a space filled with warm air in which many per- 

 sons have breathed we fill a flask and weigh it, we shall 

 find that, unless the carbonic acid is unusually great, the 

 weight is less than the weight of the same bulk of air taken 

 before it was warmed by human beings. If we shut up 

 the space and allow it to cool to its first temperature, and 

 weigh a similar bulk of air, we find that it is really heavier 

 than it was at first. Fortunately the warmth raises the air 

 above us, and it seeks an exit away from our lungs ; so 

 that air rendered in this way impure is made lighter, but 

 as soon as it cools, it is heavier than at first and falls down. 

 To ventilate well, the air must be removed before it cools, 

 and the heating, cooling, and ventilating must work in 

 harmony. It is not easy to bring these agents to act so. 



The air raised into the lantern above the court was in- 

 ferior to that below, and contained only 20*4800 of oxygen, 

 being a loss of 5Q00 in a million. Nature never seems to 

 offer us air with a loss of even 1000 in a million. Com- 

 paring healthy places with healthy, the difference is about 

 200, and perhaps this indicates a similar difference of vital 

 principle in a climate. 



I need scarcely say that I found no such loss of oxygen in 

 the mills of Manchester, or in any other inhabited place 

 above ground during the day. If we seek air similarly 

 degraded, we must. descend the shafts of mines, and there 

 we find oxygen removed in some places to a much greater 

 extent. As an average, however, the currents in a metalli- 

 ferous mine gallery contain 20'650o of oxygen, exactly the 

 amount in the court, and the air under the shafts 20*424, 

 almost exactly the amount in the lantern. I certainly am 

 anxious to see legislation in favour of miners ; but this is a 

 circumstance rather adverse to my hopes. 



