1886.] Mr Shaw, On an experiment in Ventilation. 413 



persons sitting on the raised seats under which are hot -water pipes 

 are sufficient to make the atmosphere behind the lecture-table 

 quite appreciably foul. I have in contemplation some experiments 

 to shew the existence of this circulation but I have not yet had 

 time to complete them. 



That hot air projected into cold does not rise with any 

 great rapidity is further illustrated by the steam which issues 

 from locomotives, which, although very much heated when ejected, 

 lies on a still day very little above the train level, and 

 contrasts remarkably in its behaviour with the vortex ring of 

 steam that is sometimes seen and which penetrates the air with 

 much greater rapidity. 



These considerations tend to shew that the circulation of air in 

 a room cannot be regarded as a simple case of convection current; 

 probably in many cases the result depends more upon diffusion 

 than convection. 



The ventilation of the lecture-room might be considered to 

 have been faulty in these respects : — 



(1) The hot-air Tobin T delivered its air direct to the 

 ceiling and there formed a layer ; a large part of it probably 

 escaped directly by the ventilator V. 



(2) The row of hot pipes also produced an upward current, 

 warming some of the air supplied by the cold Tobin T and 

 sending it direct to the ceiling. This as stated would be to a 

 certain extent remedied by local circulation produced by the 

 windows. 



(3) The foul air immediately over the audience probably 

 formed a circulation of its own; part indeed escaping by the 

 ventilator V, and the rest falling upon the lecturer. 



There are two acknowledged principles of efficient ventilation, 

 the first to supply fresh air in such a way that the position it will 

 take up is known, and in such quantity that it must extend 

 rapidly enough over the whole room, and then to let the foul air 

 find its way out; the second to remove the foul air by means of 

 exhaust pipes drawing air from where it is known to be foul 

 and leaving the fresh air to find its way in. In altering the 

 ventilation of the room in question I have endeavoured to secure 

 the advantages of both these methods in the following manner. 



The Tobin T forms a layer of hot air at the ceiling. I have 

 prevented this escaping by covering the ventilator V by a 

 wooden shaft attached to the wall which has an opening 24" x 14" 

 inclined at an angle of 45° to the wall about 6 feet above the 

 floor. The layer of hot fresh air must therefore gradually thicken 

 and in time fill the room (neglecting that part of it which will 

 escape unused by the ventilator V). This is the application of 

 the first method. 



