34 apparatus for affording a Standard Meafure. 



weight being all on one fide. The evident advantages of the metallic fupport 1 1 being made- 

 in the form of a tube are, that it will be more rigid than the fame mafs any otherwife difpofed, 

 and that it will more fpeedily, on account of its furface, acquire the temperature of the furround- 

 ing air. B B is a brafs fupport to which the tube C C is firmly fixed or foldered. This laft 

 tube is flit longitudinally, and fits upon the tube 1 1, fo as perfeftly to fteady it, but, at the fame 

 time, to leave it at liberty to Hide up and down with confiderably facility. A ftronger piece 

 E D F furrounds the tube C C, and when the thumb-fcrew G is tightened, Ht caufes C to 

 embrace I firmly, and confine it from Aiding at all. Imagine the tube II to be continued 

 downwards ; and at feme diftance lower upon the wooden frame of fupport there is fcrewed the 

 piece A D, fig. i. This piece, at its outer face, affords a dove-tail groove for a Aiding part, G G, 

 to move in. The Aiding part carries a piece which forms two half holes at K, which embrace 

 the tube 1 1, and hold it firmly when the thumb-fcrews L L are fcrewed up : theadjuftingfcrew 

 H H is previoufly ufed to fet the Aiding piece to any defired pofition. If we nov/ connecSi; the 

 whole together, and fuppofe the tube I to be grafped by the piece K while it remains unconfined 

 at D, in fig. 2, the whole pendulum will be raifed and lowered by the expanfions and contrac- 

 tions of the tube I I, which is above K. The centre of fufpenfion V, fig. 3, will alfo be liable 

 to feme change of place from thermometical variations of the wooden frame, and the ball of 

 the pendulum will be lowered by the expanfion of the fteel-wire from the feme changes as 

 caufed them to rife from the expanfion of the tube I I. Whatever may be the metal of the 

 tube, it is eafy to conceive, that if it be very long, its efFeiSl will predominate over that of the 

 expanfion of the wire, and, on the contrary, that if it be fliorter than a certain length, the con- 

 trary efFedt will take place. That the tube fhall accurately compenfate for the changes in the 

 pendulum is a matter of experiment or trial ; and as brafs expands more than moft other metals 

 in common ufe, it is clear, that a fhorter tube or brafs will anfwer the purpofe better than one cf 

 any of the other common metals. To make the adjuftment, nothing more is required than, in the 

 firft place, to fcrew the tube faft by the nut G, fig. 2, and aftexwards loofen the piece K, fig. i. 

 1'he Aiding piece G G may then be moved upwards or downwards, by means of the fcrew 

 H II, accordingly as the obferved efFedt of temperature upon the rate may have indicated the 

 neceflity of fliortening or lengthening the ading part of the tube. The fcrews L L, fig. i, 

 may then be again fcrewed up, and the fcrew G, fig. 2, loofened. * 



It is rather unfortunate, that neither the public;;tion of Mr. Whitehurft, nor that of Dr. 

 Fordyce, contain any regifter of the going of this clock. The former had no tranfit inflru- 

 ment, but carried his time from his neighbour, Mr. Mudge. The latter, who had miAaid the 

 particulars of his obfervations, kept his inftrument going at the vibration of feconds for about 

 nine months, during which, the thermometer had fallen as low as 15° of Fahrenheit, and rifen 

 as high as 84". The greateft difference from its rate of going was, in the words of the 

 Do£tor ; " Counting on according to the rate of its going, during the whole time, it never 

 exceeded the fum half a fecond, nor was ever lefs than half a fecond, whether it was taken from 

 day to day, month to month, or from any one to any other period during the obfervation,** 

 which, I think, is at leaft as accurate, if not more fo, than the performance of any other time- 

 piece. 



It is ftill more unfortiinate, that Sir George Shuckburgh Evelyn, in his late refearches to 



afcertain 



