In Harrison's pendulum five bars of steel and four of brass were so arranged, that they produced two expansions of brass upwards, and three of steel down wards, so proportioned to each other, that the ascending expansions fully com pensated those in the contrary direction. This pendulum has been since its inven tion generally used, where very accurate Measurement of time was necessary. A further description of it, of Elliot's pen dulum, (which wasthe next made on this plan, and differs little from it,) and of the others here mentioned, will be inserted under the article PENDULUM.
It has been supposed by several, that the tubular pendulum (which is also a modification of Harrison's compensation) is but a very recent invention : but the writer of this article having met with one by accident, which was made upwards of thirty years ago, thinks it but justice, both to the public, and the ingenious ar tist who directed its construction, to op pose this opinion. This pendulum is in possession of Mr. Patoureaux, watch and clock-maker, 15, Wardour-street. It was made by Mr. \William Brown, a clock maker well known to the trade, who has been dead upwards of five years, and who formerly resided near the Seven Di als. His brother, a jeweller, residing in 15, Coventry Court, Hay-market, was his executor, and sold the pendulum to Mr. Barrett, clock-maker, of Compton-street, some years ago, from whence Mr. Pa toureaux bought it. Mr. Brown, the jew eller, informed the writer that this pen dulum had been made by his brother up wards of thirty blears ago, just after he had served his time to Mr. Chandler, then of King-street, Seven Dials, (whom he afterwards succeeded in his business;; and that it was made by direction of Mr. Chandler, who, as far as he knew, was the inventor of it : and in corroboration of this assertion, Mr. Hampson, working clock•maker, .22, Greek-street, Soho, declares, that he made several pendulums of the same construction for Mr. Brown, upwards of seven years ago. This tubu lar pendulum, which at present we must attribute to the ingenuity of Mr. Chand ler, is composed of two tubes and a rod of iron, and two tubes of brass. The iron rod is about a quarter of an inch in diameter, and is suspended by a spring in the common manner ; it is inclosed by the first brass tube, to which it is con nected at bottom : an iron tube, sup ported by the top of the brass tube, then descends a little below it, and supports by its lower extremity the second brass tube, which rises a little above the for mer tubes, and from the top of it the se cond iron tube descends below all about two inches, into the substance of the pendulum bob, which is very large and heavy: the bottom of this last tube con tains a nut, into which a screw (having a milled head beneath that sustains the bob) passes from below, and raises or lowers the bob, as required for the ad justment of the rate of going of the clock. We may date the invention of
the tubular pendulum, from the fore going information, about the year 1775, though it may yet be found to be of a still earlier period. The foreman of Mr. Villaumy, clock-maker to the Prince of' Wales, Pall Mall, declares, that be remembers a tubular pendulum to have been made by Air. Finney, a well known clock-maker of Liverpool, up wards of forty years ago, and that it is now in the possession of Mr. De AIem bry, of Richmond, but time will not per mit the farther investigation of this point at present.
The last modification of the longitu dinal compensation made public is that of Mr. Troughton, mathematical instrument maker; it differs from Chandler's tubular pendulum, in having but two tubes of brass, which afford the ascending com pensations,while the descending ones are performed by five wires of steel. The order of brass and steel is the same as in Chandler's pendulum ; but all the steel wires pass downwards through the inter nal brass tube. The last pair of wires connect the whole with the bob by a short cylindrical piece of brass, to which the bob is suspended by its centre.
Mr. Troughton made this pendulum in July, 1804, and published the first account of it in December same year, in Nicholson's Philosophical Journal : we believe he knew nothing of the priority of Chandler's tubular pendulum to his, and that, in thinking and declaring him self the first inventor of tubular pendu lums, he only fell into an error common to many other ingenious men on similar occasions ; and this error is the more excusable, as, at the time Chandler made his pendulum, there were no periodical works in existence, which professedly re corded the improvements of arts and ma nufactures, and artists were in general more careful to conceal their discoveries, than to acquire reputation by making them public.