346 Notice regarding a Time-Keeper in the Hall 



Many ingenious contrivances have been fallen on by men of 

 science, and by mechanicians, to attain these ends, but some 

 causes of error, which appear to be inseparable from the ma- 

 terials employed, still remained to be removed. As an endea- 

 vour has now been made to get rid of these difficulties, by some 

 changes in the mechanism of the clock, and in the material of 

 the pendulum, I shall proceed to explain the peculiarities in 

 their construction. 



The principal circumstances in which this time-keeper differs 

 from the usual constructions are these; 1st, In having an es- 

 capement which requires no oil ; 2d, In having the pendulum 

 and ball formed of a material not hitherto used for this purpose ; 

 and 3d, In having the mechanism entirely secured against the 

 effects of dust, and in a great degree against those of hygrome- 

 tric changes in the atmosphere. 



First as to the Escapement. It is no doubt known to most 

 persons now present, that, in the usual forms of clock-escape- 

 ments, the teeth of the scape-wheel act alternately on two pal- 

 lets, or inclined planes, which are placed at the extremities of 

 branches proceeding from an axis, which axis has a third branch 

 or tail, by which it communicates to the pendulum the impulses 

 which it receives from the wheel- work, through the pallets. Thus 

 in Plate XIV., Fig. 1 ., which is an enlarged drawing of the most 

 commonly used escapement, A is the scape- wheel, which is urged 

 round, in the direction of the arrow, by the maintaining power 

 of the clock ; B B are the two pallets ; C is the axis from which 

 they proceed ; and D is a part of the third branch or tail, by 

 which the successive impulses are communicated to the pendu- 

 lum. 



The chief cause of irregularity in this, and in all other forms 

 of escapements where the teeth of the scape-wheel act on in- 

 clined planes, is the oil which is necessarily introduced to dimi- 

 nish the friction of the rubbing surfaces. In good clocks this 



