ENGINE-BOOM FITTINGS.
hammer is directly attached to a spring, and isacted upon by a wheel, having on its circum-ference a series of evolute cogs, the same in
Fig. 204.
MESSES, soul’s MECHANICAL TELEGEAPH.
number as the signals upon the dial. Toinsure the sudden release of the hammer, inorder that it may strike the bell effectively, apeculiarly shaped cam is mounted upon it,which, after being raised by the cogs on the’wheel to the requisite extent, allows the alarumhammer to fall and to react, without meetingwith any hindrance which might impair itsfree action should the wheel not be movedquick enough. This arrangement dispenseswith the use of several springs and hammers,without diminishing the number of the requiredsignals.
Where great lengthsof shafting are required,if is customary to connect the lengths by one
EXPANSION JOINT FOE TELEGEAPH SHAFTING.
0r more expansion joints, as shown by Fig. 205,f° admit of the extension or shortening of the
329
lengths, due to the variation in the tempe-rature, or other cause, and thus insure a properand easy action of the telegraph under suchcircumstances.
It is often found that, in mechanical tele-graphs in which there is a great length ofshafting, or a number of wheels between theoperating and indicating dials, the motion ofthe pointer on the operating dial is not com-municated in the same degree to the pointeror other revolving part of the indicating dial;and that there is a certain “ lagging behind,”or loss, due either to the twisting or torsion ofthe shafting, or the play, or what is technicallytermed “ backlash,” between the teeth of thewheels, and sometimes to both of these causescombined. The effect is, that the pointer onthe indicating dial is placed in such a positionthat it is quite difficult to discover to which oftwo signals it refers. From the same cause,when a fixed plate with a single slot is used asthe front dial, and a revolving plate with thesignals engraved thereon is employed as theback dial, it perhaps occurs that only part ofthe signal is exhibited, or in many cases parts oftwo signals, thereby creating great uncertaintyand confusion, and entirely destroying theuseful effect of the telegraph. To obviate thesedefects, Messrs. Soul have designed two dialplates, as illustrated by Fig. 206—page 330.The signals are engraved on a stationary backplate, and a slotted front plate being attachedto revolve on the shaft of the telegraph instru-ment. The revolving slots permit only onesignal, or only one compound signal, to be atany one time exhibited, while at the sametime the length of the slots and the spacelikewise occupied by the letters, comprising
3 B