348 Mr Stevenson on a new Signal- Light for Bailways. 



miles down to two or three miles ; and this evil is unhappily 

 one of those which, in the present state of chemical and opti- 

 cal science must, we fear, he pronounced irremediable. This 

 defect, great as it is in regard to lighthouses, is, in the case of 

 railways, materially aggravated hy the excessive velocity of 

 railway-travelling. Any variation in the distance at which a 

 signal-light is first seen, must lead to great misconceptions as 

 to the time of reaching a station, and all such misconceptions 

 are fraught with the worst consequences, owing to the nu- 

 merous sources of danger from the crossings of branch lines, 

 the meeting of carriages on the rails, or the occurrence of other 

 accidents, which may render a railway impassable. It is there- 

 fore obviously indispensable to safety that the signal-lights 

 should be so constructed, that in all states of the weather they 

 shall be constantly visible at the same point, and that this 

 point shall be sufficiently distant from the station, the approach 

 to which the signal is intended to announce, so as to allow 

 ample time for checking the engine's speed before coming up 

 to it ; and upon no other grounds can the confidence of the 

 public as to their security be reasonably based, f 



In the month of December last, it occurred to me in the 

 course of conversation with my friend Mr Errington, civil en- 

 gineer, that although the variation in the visibility of lights of 

 distant range must, according to our present knowledge, be 

 regarded as an evil without remedy, it might still be possible, 

 by means of some arrangement of the lights, to render signals 

 for railways constantly visible at the same point during every 

 state of the atmosphere. For this purpose, all that seems to 

 be necessary is, to limit the range of the lights, and at the 

 same time to increase their intensity in such a manner that the 

 combination of a short range with great power may not merely 

 render them capable of penetrating any fog however dense, 

 but of producing, at a certain point, an effect so brilliant and 

 striking as forcibly to arrest the engine man's attention. Af- 

 ter considering the matter in various points of view, I came 

 to the conclusion that the object could be best attained by 

 placing the light considerably in advance of the station, the 

 approach to which it is intended to announce, and by giving 

 the beam such an inclination to the horizon, that its greatest 



