TRANSACTIONS OF SECTION G. 1199 
through which ‘carriers’ containing the actual written messages are propelled. 
The system was first introduced by Mr. L. Clark in 1854, who employed vacuum, 
‘drawing the carriers in one direction only. The first tube which came into opera- 
tion was laid for the Electric Telegraph Company between their office in Loth ury 
and their branch office at the Stock Exchange. This tube was in continuous use 
for over twenty years and was in good condition when raised, 
About the year 1866 Mr. C. F. Varley applied compressed air for propelling the 
carriers in the opposite direction from that in which they were drawn by vacuum, 
and very ingenious valves were designed by him for effecting the change from 
vacuum to pressure, 
With each of the foregoing systems it was necessary after the transmission of 
a carrier to restore the pressure in the tube to the normal atmospheric pressure 
before another carrier could be despatched. This caused considerable delay and 
loss of engine-power. 
In 1870 the author designed the double sluice valve which is now in general 
use, and by means of which carriers can be despatched continuously without 
stopping the flow of air in the tube. 
The employment of pneumatic tubes in London has been continually increasing 
until the system, which in 1854 was represented by one 6 H.P. engine working a 
single tube a few yards in length, at the present time comprises four 50 H.P. engines 
{each indicating 130 H.P.) and forty-nine tubes, the aggregate length of which 
exceeds twenty-seven miles. These figures are exclusive of over a mile in short 
lengths of house tubes also worked by the engines, as well as of over a dozen hand- 
worked tubes in various metropolitan offices. The use of pneumatic tubes, how- 
ever, has not been restricted to London alone, for in the provincial cities and towns 
there are sixty-three tubes which, with the London tubes, bring the total length 
of engine-worked tubes to upwards of thirty-nine miles. To these should be added 
ninety-five shorter hand-worked tubes. With the air-pressure employed an ap- 
proximate speed of one mile in seventy seconds is attained in tubes not exceeding 
a mile in length. The speed varies inversely as the square of the length of the 
tube. The pipes generally employed are of lead, having an internal diameter of 
22 inches. 
At Liverpool a very complete pneumatic system has lately been installed. The 
number of tubes has been increased from eight to fourteen and three 30 H.P. beam 
‘engines (each indicating up to 90 H.P.) have been erected. These engines were 
‘designed and constructed under the personal supervision of the author, and were 
made by Messrs. Easton and Anderson of Whitehall Place, London, and Erith, 
Kent. The pumps are so arranged that either set can either exhaust or compress 
air. Two engines are sufficient for the present requirements, the third being spare 
in case of breakdown. 
TUESDAY, SEPTEMBER 15. 
The following Report and Papers were read :— 
1. Report of the Patent Law Committee.—See Reports, p. 695. 
2. Autographic Apparatus for Machines for Testing Materials. 
By Professor W. C. Unwin, M.Inst.C.E. 
With the increasing use of steel in construction, the necessity of recular and 
systematic testing of the elastic properties of materials has become much more 
urgent. Rough bending and temper tests furnish, it is true, useful information as 
to the quality of steel. But no procedure furnishes information so reliable and 
accurate as a breaking test, carried out by means of a suitable machine ; nor can the 
quality of the material be specified in any other way so definitely, as by requiring 
