250 Dr. J. S. G. Thomas on Thermal Effect of a slow 



decrease further at a decreasing rate the temperature rise 

 experienced by B, due to an impressed air stream. The 

 effects of the respective wires upon the temperature of B 

 may be taken as represented by the reciprocals of NP, NQ, 

 and NR, the effect of subsequent wires being negligible, 

 this being graphically represented by the fact that the line 

 BNPQE. does not meet the finite line G%'. 



The characteristics of the initial parts of the curves con- 

 tained in fig. 3, and referred to under 5 («), (b), (c), and [d) 

 above, can now be readily explained, thus : — 



Group (a). For the wires A, B, C, D, and E in fig. 5 

 the positive triangular areas drawn above the wires and 

 representing the thermal effect experienced by the respective 

 wires clearly increases as the wire in question occupies the 

 successive positions in the direction of flow of the stream. 

 The total cooling or negative effect, on the other hand, is 

 the same for successive wires from A to E. The initial rise 

 in temperature of successive wires in this group therefore 

 increases from A to E. 



Group (b). For these the initial rise of temperature is 

 less than that in the case of No. 5 wire, and is approxi- 

 mately constant. Graphically, this is illustrated in the 

 case of wire F in this group by the fact that under condi- 

 tions such that ES meets four of the lines representing the 

 hot convection currents ascending from the wires, the line 

 FT would meet three only*. The wire A is, in fact, so far 

 away from the wires included in this group that its re- 

 latively small free convection current is without influence 

 upon the wires in this group. For succeeding wires of this 

 group the effect of the free convection current arising from 

 B is in like manner negligible. Thus FT, GIT alike cut 

 three of the lines representing the hot convection currents 

 arising from the wires. Obviously, owing to the skew 

 nature of the diagram fig. 5, the wires constituting this 

 group will be unsymmetrieally placed with respect to the 

 central wire of the series, and will be grouped about a point 

 to the left of that wire. 



Group (c). For this group, constituted of wires 8, 9 and 

 10, the initial rise of temperature progressively increases as 

 in group (a). This is to be attributed, as shown in fig. 5, 

 to the decreasing number of cold convection currents rising 

 towards the wires to the left of the respective wires. The 



* It is clear, that if the diagram were correctly drawn with special 

 reference to this case, Aa would be shown so that angle aAB < angle 

 3BC, on account of lower temperature of wire A. Aa would then meet 

 ES, although FT would not meet B/3. 



