7S ON PEWDULUMS, 



pend,) that the refult will be the fame in every different tem- 

 perature; Bmay alfobe formed of two cycloidal plates, having 

 circular grooves hollowed on their edges, and A have two 

 projecting circles turned on it to run in thofe grooves; the me- 

 thod of connecting A with the clock-work may alfo be varied 

 many other ways. 

 Concerning fiic- Before I conclude, I beg leave to obferve that the method, 

 tion, &c before mentioned, of preventing friction in the motion of the 



fphere in the parabolical trough, might be applied very bene- 

 ficially in the conftruction of rail roads, by forming the upper 

 part of the rail of a femi-cylindrical (hape, and making in the 

 edges of the wheels, (which were to run on them,) circular 

 grooves, whofe diameters mould each exceed that of the rail; 

 in the ufual way of forming rail-roads, the lateral friction to the 

 wheels 'is very confiderable, whether they have flanches to 

 them, and the rails are made plain, as in the Swanfea roads; 

 or the rails are formed with rifing ledges, and the wheels plain> 

 as in the Croydon road. 

 The circular I fliall a!fo requefr. permiffion to mention, in addition to your 



pendulum a good note 0n p ron y's condenfer of forces, that a regulator might be 

 regulator of fir ft f , . J . . . ... . . , , ". „ 



movers. formed on the principles or the circular pendulum, as tig. 3, 



which would temper the motion of wind-mills, or other en- 

 gines, and react on them in return, (as well as the fly wheel)* 

 in a much more fimple and effectual manner than the very com- 

 plicated apparatus defcribed by Prony for the fame purpofe, 

 and which feems to me moreover peculiarly liable to be broken 

 by any .fudden increafe of velocity in the mill, unlefs formed of 

 nioft cumberous ltrength. 



I requeft the favour of having the following typographical 

 errors noted in the paper on my tallow lamp. November, 

 180i, page 147, line the eighth, for the word frefh, read 

 freely-, and line the 25th, fame page, between the words 

 Tweans and horizontal, infert the letter P. In the plale alfo, the 

 pan mould be deeper and larger than there reprefented, and 

 the tallow bolder more central. 



I am, Sir, 



Your very humble fervatir, 



J. WHITLEY BOS WELL. 



Reference 



