356 Mr. S. Tolver Preston on Method 



A single circuit was arranged as shown in fig. 3, 

 Fig. 3. 



T and T' are the telephones, H is the double helix. The 

 helix was joined up as shown in the figure, one end of each 

 of its wires, a and b, being left unconnected and insulated. 

 Thus arranged, there was a break in the continuity of the 

 circuit, but nevertheless speech was transmitted with perfect 

 distinctness, and conversation carried on with the same facility 

 as in the previous experiments, the helix acting not as a con- 

 ductor, but as a condenser, its two wires replacing the two 

 sets of plates ; and it made no difference which of the ends 

 of the wires of the helix were connected to the line-wires, or 

 whether the currents entered the wires of the helix in the 

 same or in opposite directions. 



The helix in the last case having been replaced by a con- 

 denser, the other arrangements remaining unaltered, speech 

 was again transmitted with as much facility and clearness as 

 if the circuit had been complete — the capacity of the con- 

 denser, which was one microfarad, being amply sufficient to 

 allow conversation to be carried on. 



XLYI. On Method in Causal Research. 

 By S. Tolver Preston*. 



A POINTED reflection as to the "danger of forgetting 

 that mathematical reasoning can only lead to useful 

 results when founded upon definite physical conceptions " f, 

 deserves, no doubt, to be fully indorsed ; and nowhere per- 

 haps could this remark be said to be more justly applicable 

 than to the problem of the constitution of the aether, which 

 may be regarded as underlying the basis of the science of 

 optics. No one, of course, would for one moment underrate 



* Communicated by the Author. 



t ' Nature,' vol. xxi. p. 370 (letter of correspondent). 



