Heat from a Pair of fine heated Wires. 283 



In the case of all dispositions of the wires, one contem- 

 plates the temperature of the accumulated hot layer of air, 

 due to any one wire, as being greatest vertically above the 

 wire, and diminishing right and left of the wire. Now, if 

 the wires be considered as so widely separated that the accu- 

 mulated layers due to the respective wires just overlap, it is 

 clear that the effect of an impressed stream of low velocity 

 would be to displace away from above the second wire the 

 hot central portion of the one accumulated layer of hot air, 

 and to bring up the comparatively colder border region 

 of that due to the first wire. The net effect, on this account 

 only, would be a considerable fall in the temperature of the 

 second wire. If, however, the wires were so close together 

 that considerable overlapping of the respective accumulated 

 layers of hot air occurs, then any similar displacement of the 

 central hot region of the accumulated hot strata above the 

 second wire is accompanied by the convection thereto of 

 the central hot region of the strata originating in the first 

 wire. The consequent fall of temperature of the second 

 wire is therefore less in this latter cnse than in the former. 

 Considering the forced convection from the wires, it is 

 readily seen that the net rise of temperature must therefore 

 be greater in the latter than in the former case. The effect 

 of the displacement of the comparatively stagnant accumu- 

 lation of hot air above the wires therefore tends to be reduced 

 as the wires approach one another, and consequently the 

 temperature attained by the second wire due to an impressed 

 stream of small velocity tends to be conditioned to an in- 

 creasing degree by the convection of heat from the two 

 wires alone. 



The last group of curves is constituted of K and L. The 

 curve L, like the curve K, possesses considerable symmetry. 

 With closer approach of the wires to one another than that 

 corresponding to K, the maximum increase of temperature 

 of the second wire diminishes. That an effect of this nature 

 must occur is clear from the consideration that when the 

 distance apart of the wires is zero, i. e. the wires are coinci- 

 dent, no liealing effect due to the impressed stream can be 

 experienced by either wire, the calibration curve then 

 assuming the form M. In the case of distances apart now 

 being considered, these are so small, that due to an impressed 

 stream the approach towards the second 'wire of the con- 

 vection current arising from the first wire is likewise small. 

 The consequent increase of temperature of the second wire 

 due to such approach will therefore be small. Moreover, as 

 the magnitude of the approach in question is proportional to 



