77 
1917-18.] Studies in Clocks and Time-keeping. 
pendulum through the suspension spring, by bending it a measured amount ; 
this method is employed in the clock Riefler. An imperfect approximation 
to the first method is supplied by the Graham dead-beat escapement, of 
which the observatory clock, Dent, No. 1506, is a not very modern example. 
Reference may be made to it occasionally, as also to a second Synchronome 
clock courteously placed at my disposal by the Synchronome Company for 
experimental purposes. 
I now pass to a description of so much of the practical details of the 
three chief clocks, Riefler, Synchronome, and Cottingham — or as they will 
occasionally be denoted, R., 2., and C. — as will be necessary to make 
reference to them intelligible, premising that this description is not in- 
tended in any sense to be complete, and does not even refer to many 
features which are essential to their good performance. 
Beginning with Riefler, our clock is No. 258, and quoting Riefler’s list, 
is of the type D, with pendulum Jl. The construction of its details is 
given in the publication, S. Riefler, Prdzisions-P endeluhren . . . Mtinchen, 
1907, and elsewhere.* Passing over anything to which I do not at present 
require to refer, it may be mentioned that the pendulum suspension spring 
is attached for support to a cock which is not fixed, as is otherwise the 
invariable rule, but rests upon knife-edges so that it can be rocked through 
a measured small angle in the plane of the motion of the pendulum. This 
motion is conveyed through an anchor, fixed to the cock and carrying 
pallets or impulse- and locking-stones upon which the teeth of the scape- 
wheel bear. For a short distance beyond the vertical position the spring 
remains straight, the pendulum and supporting cock rotating as one piece 
upon the knife-edges of the latter ; for a part of this time the train moves 
freely ; then the scape-wheel comes into contact with the impulse-face of 
the pallet, quickly twists the cock back to the vertical position and locks 
itself, leaving the pendulum to swing on freely to the end of its arc with 
the added energy of the bent spring ; the direction of bending is opposite 
to the motion of the pendulum, and therefore locks the scape-wheel securely 
until the pendulum upon its return again reaches the vertical position ; 
hence it is possible to minimise the friction of the unlocking without risk 
of the movement tripping or escaping prematurely, and so the angle 
between the locking-stone and the scape-wheel teeth is made the angle of 
sliding friction. The overlapping portion of the scape- wheel tooth in contact 
is also very small. The pendulum swings freely, from the locking position 
in which the cock and anchor are set back into their vertical position, up 
to the unlocking position of the next semi-oscillation, which may be taken 
Gf. Ambronn, Handbuch d. Astronomischen Inslrumentenkunde , Bd. i. (1899), p. 200. 
