.s7A' WILLIAM SIEMENS, l-'.R.S. 351 



to the expanded and cooled air ; but towards the end of the 

 tr.msit iiu work, excepting frictiou, had to be performed and all 

 the heat that had been picked up by the air in the early part 

 of its transit would appear in the form of additional free heat at 

 tin- cud. After this explanation, he hoped that the authors would 

 with him that the co-efficients in their formulae, taken from 

 the dynamical action of expanding air, were not applicable. It 

 might In- mentioned that the experiments given at the end of the 

 u.ip'T exactly continued his view. In other respects the theoretical 

 considerations involved in this subject had been put forward in a 

 complete and elegant manner, and some of the experimental results 

 were extremely valuable. 



Regarding a comparison of the radial with the circuit system, 

 he believed that the advantage was with the latter. The radial 

 system implied a greater number of tubes ; and it was, therefore, 

 wasteful in point of cost. It implied, if the radii were worked 

 on the continuous system which was almost necessary where there 

 was so large a traffic as in London a greatly increased con- 

 sumption of compressed or rarefied air, as the case might be. 

 Moreover if there were, say, twenty or thirty stations round the 

 central station it would be practically impossible to lay as many 

 tubes radiating from one centre, each tube consisting of a leaden 

 pipe surrounded by an iron one. The streets would not be suffi- 

 cient to contain such a number of tubes. Although the radial 

 system might do for collecting messages from offices in the im- 

 mediate neighbourhood of the central station, he felt sure that 

 whenever the time came for the establishment of the pneumatic 

 despatch system on a large scale, requiring larger diameters and a 

 combination of hundreds of stations (so that a parcel could be sent 

 from any one station to any other), it would be impossible to carry 

 out such an object by the radial system, and a return to the circuit 

 system would be absolutely necessary. 



])H. Si KM HNS said he desired to congratulate the Institution 

 upon the very lucid explanation and scientific expose of Professor 

 di win, with every word of which he agreed. He had already 

 discussed Mr. Sabi ne's paper, but now proposed to offer a few 

 remarks on the theoretical principle involved in M. Bontemps' 

 communication. An interesting account had been given of 



