16 &* THK IRREGULARITIES OP TIME. 



A gentleman informed me lately, that rooks alio eat the 

 beetles. 



But thefe means are confined to* the winged beetle. It 

 appears to me that the mole is the only certain deftroyer of 

 the grub. 



My hay and pafture grounds are, every fpring, thickly 

 fhulded with mole hillocks. They are fcattered in the ufual 

 manner; and when the gralfes are up, the moles ceafe to 

 work, and fcarce a hillock appears till after harveit. 



VI. 



Methods of diminifhing the Irregularities of Time-Pieces, arifing 

 from differences in the Arc of Vibration of the Pendulum. By 

 Mr. Ezekiel Walker. 



To Mr. NICHOLSON. 

 S I R, 



Lynn Regis, May\l, 1802, 



Chronometers, /\fTER all the improvements which the mechanifm of 

 &c. rendered ir- . - ■ • i i nn » r t 



regular by the clocks and watches has received, there are lull obftacles 



°ih which fland in the way of an exa& performance. The ufe of 



oil in chronometers has long been complained of, but ftill re- 

 mains a neceflary evil ; and that variation which obtains in the 

 arc of vibration of the pendulum, is a fource of much error in 

 clocks. 

 Tranfit dock at The tranfit clock at Greenwich fometimes varies in its femi- 

 riesin its arc of arc °f vibration twenty minutes in a year, and a compound 

 vibration. pendulum which came under my own infpeclion fome years 



ago, varied in its arc nearly as much. 

 Old remedy for Many years have elapfed fince it was difcovered, that the 

 the arcs ty mort v i Drauons vvere performed in lefs time than the long ones, 

 and methods were ufed to remove the inconvenience. Huy- 

 gens propofed a method by which the centre of ofcillation 

 might be made to vibrate in the arc of a cycloid, and demon- 

 ltrated that a pendulum moving in that curve, would perform 

 all its vibFations, whether long or fliort, in equal times : and 

 others propofed to remove the evil by a peculiar form of the 

 pallats. 



Thefe 



