▼OL. XLVII.] PHILOSOPHICAL TRANSACTIONS. 377 



error, which it was a considerable time before he discovered, his making the 

 trial was thereby greatly retarded. And in order to prevent others from falling 

 into the like mistake, he gives the following short account of it. 



In a common clock, the pendulum is usually hung by a spring to a cock on 



the back plate of the clock, while the wheel and pallets, by which the pendulum 



is kept in motion, are placed in the middle of the frame ; and the pendulum is 



moved by a piece of steel, called the crutch, riveted to one end of the arbor, to 



which the pallets are fastened. This disposition of the pieces he apprehended 



liable to some considerable objections : to remedy which, he contrived to fix the 



pallets to the upper part of the pendulum itself, above the centre of motion ; and, 



in order to make the pendulum vibrate as freely as possible, it was made to turn 



on two steel points, and was hung in the middle of the frame, exactly under the 



swing-wheel, and so as to vibrate in the same plane with it. By this means he 



was in hopes, that it would have moved with much greater freedom and regularity, 



than when hung after the common method ; and on trial it was found to move 



with so great freedom, that a pendulum of above 20 pounds weight, when hung 



in its place without the clockwork, and made to vibrate through an arch of 2 



degrees, was found to make above 1200 vibrations, before it had lost half a 



degree, and was observed to have a sensible motion above 20 hours afterwards ; 



and the clock, when first put together, was kept going, for several days, by a 



weight of only 1 1 ounces, hung to the end of a single line. But it was not long 



before he discovered, that this great freedom made it liable to be considerably 



affected by the least motion. A remarkable instance of this he communicated to 



this Society, which was published in the Philos. Trans. N° 453. But the 



greatest objection to this method was, the points being subject to wear ; and he 



found that the least alteration in them would occasion the clock to vary much 



more than he could have imagined. To remedy this inconvenience, he made 



the pendulum to move upon edges, like those on which the beam of a pair of scales 



turns ; but he found these likewise liable to wear, though not in so short a time 



as the points ; so that, after much time spent in making several experiments, in 



order to remedy this inconvenience, he found himself obliged to lay this method 



wholly aside, and to hang the pendulum on a spring, as usual. 



This alteration being made, he found that the clock went very regular ; and, 

 after a sufficient trial, he was fully satisfied the pendulum would answer his expec- 

 tations. But, fearing lest he might be thought prejudiced in favour of his own 

 invention, he engaged the Rev. Mr. Professor Bliss to make trial of it ; and ac- 

 cordingly, in the beginning of the year 1750, he sent to him, at Oxford, a clock 

 for that purpose ; and in January last he received from him a letter, giving his 

 opinion of it, of which the following (so far as relates to the clock) is an exact 

 copy. 



