275 
TEAIM-SIGNALLING IN THEORY AND PRACTICE. 
BY CHARLES V. WALKER, F.R.S., F.R.A.S., 
TELEGEAPH ENGINEER TO THE SOUTH EASTERN RAILWAY COMPANY. 
K x> 
T he object of this conmninication is to give tbe reader 
a basty peep bebind tbe scenes — to introduce bim to 
certain silent operations tbat are, bour by bour and minute by 
minute, being carried on in bis interest, but wbicb, for tbe most 
part, are known to bim only in tbeir results. But bow these 
results are brought about with accuracy so unerring is but 
little understood by bim; and there is no marvel in this. Tbe 
reader to whom I refer is, of course, a railway traveller; 
every one travels, more or less, bebind tbe steam horse on tbe 
iron road. In early days, when trains were few and far 
between and tbeir pace was slow, tbeir movements could be 
regulated with tolerable facility, and without tbe application of 
any very special processes. At tbe present time — so intricate 
has become tbe network of railways, so complicated tbe roads, 
tbe stations, and tbe junctions, and tbe trains themselves so 
formidable in number and so mixed in character, tbat nothing 
short of special appliances, simple in tbe extreme themselves,, 
complex apparently in tbe aggregate, are found adequate to 
secure tbe safe and convenient conduct of tbe gigantic railway 
tra.fiic of tbe present age. It is true tbat tbe trains of to-day 
—express, tidal, and such like, move along with what our 
grandsires would, indeed, have regarded as fabulous rapidity — - 
forty, fifty, sixty miles an bour; but we have tbat which 
moves far more rapidly than these — by comparison slow- 
coaches — I mean, of course, electricity. Wheatstone was tbe 
brst to measure its velocity, and found it to be 288,000 miles 
in a second ; this is its most rapid rate of motion. When tbe 
Atlantic cable lay at Keybam Yard, Devonport, in process of 
being coiled into tbe bolds of tbe Niagara and tbe Aga- 
meimion, I repeatedly measured tbe rate at wbicb electric 
signals travelled, and found it to be about 1,000 miles 
per second; wbicb is one of tbe slowest, if not tbe slowest, 
rate of travelling on record; and slow, though this by com- 
parison appears to be, it is a thousandfold faster than tbe 
fastest of express trains ; so tbat, if we send electrical impulses 
VOL. TV. — >:0. XV. u 
