Manchester Memoirs, Vol. liii. (1908), No. 5. 9 



and it will be noticed that this increase becomes generally 

 more marked as the intensity is reduced. It seems 

 reasonable to infer from this that the proportional 

 increase will be at least as great, and probably much 

 greater, when the intensity is reduced to the amount 

 obtaining in front of an ordinary fire grate. 



In Experiment V. the average increase, over a circle 

 of 2" diameter having the poker as centre, was practically 

 50%, and even if the local increase in front of the fire 

 grate is no greater than this, it would certainly, under 

 favourable conditions, be more than sufficient to account 

 for the beneficial effect of the poker. 



The explanation of the phenomenon would appear to 

 be found in the fact that when a current of air impinges 

 on a fixed body, eddies are formed on its leeward side, 

 where a region of low pressure (below that of the 

 atmosphere) in consequence exists. There is a tendency 

 to inward flow towards this from all surrounding regions, 

 accompanied by a consequent inward and upward flow 

 towards and along the under side of the poker and 

 towards the fire, this taking place along its whole length, 

 but particularly from its lower end which is shielded from 

 the direct influence of the draught. 



In addition to this the air which is deflected by 

 immediate contact with the upper surface of the poker 

 tends, in virtue of its viscosity, to induce a secondary 

 current in the same direction in the surrounding air. 



The net result of these combined actions is that a 

 larger volume of air passes the region immediately 

 surrounding the poker, than when the latter is not in 

 position, its direction of flow being brought more nearly 

 parallel to the latter. At the same time the intensity of 

 flow at points more remote is, of course, correspondingly 

 reduced. 



