1886.] Mr Shaw, On an experiment in Ventilation. 411 



municates directly with the outside air, and consequently delivers 

 cold air. 



The ventilators V, V are not far from the middle of the two 

 end walls ami close to the ceiling. 



The accepted theory of ventilation upon which this arrange- 

 ment is based is that a source of heat in the room warms the 

 air, which rises to the ceiling and passes out by the flues of the 

 ventilators V, V. The sources of heat in the room in question 

 may be taken to be the lecture class. The air which they have 

 used will according to this theory rise to the ceiling and be drawn 

 out by the ventilators as desired, its place being supplied by fresh 

 air delivered by the Tobins. 



Other sources of heat which should produce a like effect 

 are the hot-water pipes; these, by the simple application of the 

 theory, should cause the air near them to rise and pass out by the 

 ventilators in like manner. That this is not the case is clearly 

 shewn by the fact that the room is rather more than comfortably 

 warm; but the row of windows above them would produce an 

 opposing downward current and may very easily account for the 

 diffusion of the hot air produced by these pipes. 



The general theory of ventilation has been illustrated by 

 various lecture-room experiments and I found some additional 

 ones in endeavouring to trace the course of the air which 

 the Tobins T, T supplied to the room. For this purpose I 

 used a gold-beater's skin balloon filled with gas only to such 

 an extent as to make it as nearly as possible of the same density 

 as the air of the room. On placing this over the Tobin T, 

 which delivered warm air, it rose at once to the ceiling and very 

 slowly made its way along there, so that we may conclude that this 

 air passed at once to the ceiling and there formed a warm layer. 

 The cold air from the Tobin T on the other hand carried the 

 balloon downwards to the floor at once and it then passed along 

 the passage towards the door at C. If placed close in the corner 

 over the Tobin, the current of incoming air raised it about 3 feet 

 and then carried it over, but the impression conveyed was that 

 the air behaved very much like water flowing over the top of the 

 Tobin. 



I did not find it possible by means of the balloon to trace the 

 course of the air far along the ceiling or floor respectively. The 

 only other additional current was one from the passage up the 

 stairs leading into the room. At the ceiling over the seats the 

 air seemed almost motionless but the fact that the ventilators 

 were active was amply evidenced by the balloon being firmly 

 held against them when brought near to them. 



It would appear therefore that, whatever happens to the 

 vitiated air, in actual practice and in accordance with the usual 



