WILLIAM SIEMENS, F.Jf.S. 319 



In the ifixi'iission of the Paper 



"PNEUMATIC DESPATCH TUBES: THE CIRCUIT 

 SYSTEM," 



By CARL SIEMENS, M. Inst. C.E., 



Mr. C. W. SIEMENS * said he would point out the leading 

 features of this system as compared with other pneumatic systems, 

 which had been in use for many years. In sending a carrier 

 through a pipe on the old system, the pipe was entirely occupied 

 by that carrier ; and, if the carrier was sent back by suction in 

 the same pipe, double the time of transit would be occupied. 

 That was sufficient for short distances ; but for greater distances 

 the working capacity of the tube became very small, because the 

 piston Telocity of a carrier in a tube of small diameter would not 

 exceed 1,000 or 1,200 feet per minute ; therefore, in a tube 

 several thousand feet long, the time occupied in sending a carrier 

 and receiving one back would be considerable. Now it had 

 occurred to his firm, that if a line could be made continuous 

 (instead of sending a carrier and waiting for the return carrier to 

 be despatched through the same tube, or even another tube), in 

 that case the carrier would form, as it were, part of the current of 

 air rushing through the entire circuit, and any number of light 

 carriers might follow each other without inconvenience, and largely 

 increase the working capacity of the tube. Moreover, it occurred 

 to his firm that, with a continuous circuit, intermediate stations 

 might be introduced for shunting out and putting in carriers to 

 be sent forward in the same circuit, whereby a multiplicity of 

 tubes, otherwise necessary, would be avoided. Four or five years 

 ago he made a proposition to the Postmaster-General to apply this 

 system to the transmission of letters, but it had not been carried 

 out, though, probably, at a future time, the project might be 

 seriously entertained. By such a system the despatch of letters 

 would, unquestionably, be much accelerated, and he should be 



* Excerpt Minutes of Proceedings of the Institution of Civil Engineers, Vol. 

 XXXIII. Session 1871-1872, pp. 16, 17. 



