In the generality of cases, there is one position of the switches, or shunts, which is necessary for the thorough or principal traffic, and in which direction the trains have to pass at a maximum velocity, while the change that is given by the other position of the switches is less frequently required, and is chiefly passed over by trains at a slow rate. The principal object of Mr. Hawkshaw's invention is, to secure the switches being held or kept in a proper position at all times for the principal or thorough traffic; and when there is occasion to transfer the trains or engine, etc. to another line from that on which the chief traffic passes, it has to be done by some person holding the switch protector in a proper position for that purpose; and immediately after such transfer from one line to the other has been effected, he lets go his hold upon the handle of the apparatus, and it will from its self-acting construction, instantly and of necessity return to its original position; moving at the same time the switches or double rails in connexion therewith in the right direction for the principal or thorough traffic, and maintain them in that position, so as to prevent the possibility of the main lines of rails being left unconnected.
In the subjoined illustration of the invention, Fig. 1. is designed.to show a front elevation, but with the front plate removed to exhibit the interior mechanism; and Fig. 2. is a side elevation at right angles to the former. It will be apparent that by depressing the lever e into the horizontal position, the bevelled wheelf, on its axis g, will actuate two bevelled pinions h and l, the lower one h turning on the vertical spindle i, the other end of which carries an eccentric, d, that turns the switch or double rail placed in connexion therewith, (but not introduced into the drawing,) in the exact position required for directing a train out of the main into a diverging line: at the same time the upper pinion l, through the medium of its vertical spindle n, turns a signal disc o into the position delineated in Fig. 1., which is at right angles with the direction of the main line. The depression of the lever e produces a third effect, that of raising a counter balance weight k, which is keyed to the axis g; so that when the train has passed into the diverging line of rails, the attendant has only to suffer the weight to operate, which brings the lever e into the vertical position again, and thereby places the signal disc o in its former edgewise position, indicating that the main line is open for the passage of trains.
When the continuity of the main line is broken by the positidn of the switches, the attendant is necessarily there attending it, and the signal also shows to the engine-man of an approaching train that such is the case, in time for the shutting off the steam, and the application of the drags. But as the reconnecting of the main line does not depend upon the vigilance of an attendant, but is forcibly self-acting, the risk of accident from the erroneous position of the switch mechanism is reduced almost to an impossibility. To render the signal visible at night, a lamp is placed in the centre of the disc. [London Journal, October, 1839.]