3 Qi\v,^o^, Drmiglit produced by an Indhied Rod. 



of the grate, its upper end being well out in the room. 

 Under these circumstances the presence of a distinct 

 current, travelling upwards and outwards along that side 

 of the poker nearest the fire, became apparent, being made 

 visible by the smoke which was drawn from the fire at 

 the tip of the poker and travelled up to within one or 

 two inches of its upper end before breaking away. 



This suggested the possibility and indeed the 

 probability of a similar current being produced when the 

 poker is inverted. If such is the case, and if the draught 

 or velocity of inflow of the air is thereby locally increased 

 to any appreciable extent, its efficiency for the purpose 

 outlined must be granted. 



The matter seemed so interesting that an attempt 

 was made to test this by measuring the velocity of inflow 

 at various points with and without the poker in position. 



For this purpose a small " Reynolds " differential 

 draught gauge was prepared and was used in connection 

 with a double Pitot or Darcy's tube. The draught gauge 

 uses oil, s.g. "90, and water as its working fluids, 7-5 inches 

 of a movement of their surface of separation being 

 equivalent to a difference of pressure of i inch of water. 

 The Darcy gauge consists of two fine glass tubes -05" 

 outside diameter, with extremely thin walls and bent so 

 that their orifices face in opposite directions and are in 

 parallel planes 7 of an inch apart. When placed parallel 



to the current this chives a direct measure of k- , where v 



is the velocity of the current, and k, though not determined 

 for this gauge, is probably not far from unity. 



On testing the combination it was, however, found to 

 be insufficiently sensitive to give an indication of the 

 draught in front of the fire great enough to enable 

 any quantitative observations to be made, while the 



