272 THE ADMIRALTY TELEGRAPH. 



exactly in their movements, and place them precisely in their required 

 positions, which cannot be done by the old machinery with cords, 

 because these are liable to expand or contract, by wet or dry weather. 

 The machinery for the set of telegraphs at the Admiralty, was constructed 

 in the most substantial manner by Maudolay, in 1816. The following 

 is an exact description : L. M. is a tall mast of an hexagonal form, 

 framed up from six fir planks put together at the angles, and bound by 

 iron hoops at different places, so as to be hollow within. The lower end, 

 L., terminates in a pivot, and the mast is retained in a vertical position 

 by a circular collar at 0., which embraces it, anJ is supported in the 

 roof of the building. The two arms P. M. and Q. R., are moveable upon 

 centres, one at the top of the mast and the other half way down. 

 When the arms are placed in a vertical position, they shut up in the 

 hollow of the mast so as to be entirely concealed ; and for this purpose 

 two of the six sides are cut a\vay at the upper part, so as to leave an 

 opening through the mast of sufficient width to allow the two arms to 

 work into it. 



To communicate motion to the arms, a small toothed wheel is fixed 

 upon each at the centre of motion, and close to its side. The teeth of those 

 wheels are actuated by endless screws or worms, formed on the upper 

 ends of the long spindles d. e. and/! g., which descend to the bottom of 

 the hollow mast, and have small levelled wheels upon them. These 

 again are acted on by wheels of similar size, fixed on the ends of short 

 horizontal spindles, which have handles, p. q,, applied at the extremities. 

 By turning the latter, motion is given to the vertical handles d. and 

 /", and by means of the endless screws upon the ends of them, 

 the wheels at M. and R., on the centres of the arms, are turned, 

 and the arms are put into any required position. But in order that the 

 people below may at all times know exactly what positions the arms 

 stand in, two dials, m. and w., are placed on the lower part of the mast, 

 each of which turns round with a motion exactly corresponding to that 

 of the arms. Each arm, therefore, has four positions in which it will 

 express different signals; and these positions are all made with the pointer 

 at an inclination of forty-five degrees from the horizontal line. These 

 signals either express the letters of the alphabet or the numerical 

 characters, according to previous arrangement, which must be made 

 known by exhibiting a preparatory signal before the communication is 

 begun. The signal to prepare for receiving letters, is by extending the 

 lower arm horizontally to the right; and for the numerals, both arms 

 are extended horizontally to the left. The arms are made with boards 



