1871.] Pneumatic Transmission. 313 



has become more perfected than it is at present. One new fea- 

 ture which Mr. Siemens proposes to introduce is a novel 

 kind of blower, which he has designed, to be worked direct 

 by the steam from a boiler, without the intervention of ma- 

 chinery, and which will not only effect a considerable saving 

 in the first cost of the requirements of each station, but it 

 will also be much more economical in working and for 

 maintenance. 



The methods adopted at the different stations on any 

 pneumatic line differ, of course, with the various methods 

 employed for transmission, and it is in this that very great 

 improvements have recently been introduced by Mr. Siemens. 

 We have stated that in the Berlin pneumatic despatch sys- 

 tem two tubes are placed parallel to each other, and con- 

 nected together at one end by a transverse coupling, whilst 

 at the other they terminate in two reservoirs, between 

 which an air-pump exhausts the air from one and com- 

 presses it into the other, by which means a continual circuit 

 is maintained, and provision is made for the dispatch of 

 messages in either direction. The tube for transmitting a 

 carrier from any station is connected with the pressure re- 

 servoir, beyond which connection it is continued at a slight 

 incline in which are placed two cocks, at an interval equal 

 to the length of the carrier. Beyond the second cock the 

 tube is open at the top in the form of a trough, into which 

 the carrier is first placed. The first cock is then opened, 

 allowing it to pass down the tube as far as the second cock. 

 The former is then closed again and the latter opened, 

 whereupon the carrier descends the inclined tube until 

 it passes the pipe communicating with the pressure reser- 

 voir, whereupon it is caught by the current of air and blown 

 to its destination. These carriers are thin metal cylinders, 

 nearly filling the tube, supported by four wheels, two at 

 each end, and alternately at right angles to each other. The 

 receptor consists of a square box placed in continuation of 

 the tube connected with the exhaust reservoir, with 

 which it communicates by means of a cock bored to the 

 same diameter as the tube itself. This box is lined with 

 brushes, through which the carrier forces its way, and its 

 impetus is thus checked, whilst at the extreme end is an 

 india-rubber buffer. The Exchange station, at the other 

 end of the tube, is supplied with similar apparatus, only, of 

 course, without the engine, pump, &c. ; instead of which the 

 tubes are connected together by a short coupling tube. In 

 some experiments which were made to determine the rela- 

 tive pressures in the two reservoirs, it was found that with 



VOL. VIII. (O.S.) — VOL. I. (N.S.) 2 S 



