TRANSACTIONS OF SECTION G. 877 



considering the relative position of the wheels of the carriages to the rails over 

 which they travel. 



It remained, therefore, only to explain the manner in which it is arranged 

 that the driver of each train shall be informed of the possible stoppage of the 

 train in front of him. 



Under normal conditions no second train will leave the station at Manchester 

 or Liverpool until the first has reached Wan-ington, a distance of over 17 miles. 



The line will be subdivided for the purpose of signalling into eight sections 

 of 4'3 miles each. As a train leaves Manchester or Liverpool a danger signal is 

 put up automatically at that station, and a second similar danger signal is put 

 up in the same way at 4-3 miles off, the first remaining at danger. The train travels 

 on until it reaches 8-6 miles, when it puts up a third danger signal, and simul- 

 taneously the signal is lowered at Manchester or Liverpool, so that the second 

 train can now leave. 



Assuming that the first train has met with an accident after passing the point 

 distant 8 6 miles, the second train would travel at full speed until it passes point 

 4'3 miles. The danger signal at that point not having been removed by the first 

 train, as it never reached point 13 miles, the driver of the second train would be 

 informed that the first train had met with an accident between 8-6 miles and 13 

 miles, and therefore that he has to slow down, but that for such lowerin<r of his 

 speed he has a clear run of over four miles. Therefore, there could be no difficulty 

 in stopping without iising the brake at all by simply cutting off' the current. 



Whenever a train passes over a point wlaere the danger signal is put up this is 

 reproduced, either electrically or mechanically, by a very simple and inexpensive 

 contrivance in the cabin of the driver, so that he would be perfectly able to see it 

 without difficulty even if there was a thick fog. 



Under these conditions of travelling it seems, therefore, superfluous to have any 

 emergency brakes ; and though it will be possible to stop the trains within 500 

 yards, no "ease can be imagined in which it would be useful or necessary to resort 

 to such a stoppage. 



A six minutes' service of trains could be established without any alteration i u 

 the proposed arrangement, and if a three minutes' service was required the blocks 

 would have to be reduced to two-mile sections, giving a clear run of two miles in 

 case of a breakdown. 



4. The Construction of Large Dynamos, as exemplified at the Paris 

 Exhibition. By Professor S. P. Thompson, F.R.S. 



5. Recent Tramway Constritction. By W. Dawson. 



G. Measurement of the Tractive Force, Resistance, and Acceleration of 

 Trains. By A. Mallock. 



The author described in the paper some experiments recently made on electric 

 and other railways, the object of the experiments being to determine the accelera- 

 tion, tractive force, and running resistKUce to which the trains are subjpct. 



The appli;ince used wms a short pendulum whose free vibrations are adequately 

 damped. It' this is suspended on the moving body it will hang in t'le direciion 

 which is the resultnnt of gravity and the acceleration which the b'dy at tlie time 

 experiences; hence the an^'-le which such a pendulum makes with the vertical 

 gives t'le measufe of the accelerations at ea h instant. 



Ill the exp.-riinents the pendulum was arrangeil so as to record its posit'on on 

 uniformly moving paper, on which at the same time seconds were marked by an 

 .elective clock, and a contact marker, worked from one of the wheels of the carriage, 

 Cfiused a second pen to record each revolution performed by the wheel.. The 



