225 



KEW PENDULUM. 



Tubular pendu. 

 lum. 



Itiftson the 



principle of the 

 gridiron. 



Defcription of 

 the tubular 

 pendulum by 

 the drawing. 



the fubjed is tlill agreeable to me, being yet unincumbered 

 with patents, the reafon of which no doubt fs, that the few 

 wanted holds out no profpecl of gain. 



Under thefe circumftances, I offer you the following de- 

 fcription of my tubular pendulum, which I contrived about (he 

 middle of laft July, and which I have juft brought into a6lion. 

 The honourable mention which you made of my mercurial pen- 

 dulum (Phil. Journal for May 1797) the excellent papers which 

 you have ai different times given to the public on this fubje61, 

 and its importance to practical fcience, efpecially aflronomy, 

 leave me no room to doubt but this communication will be 

 agreeable to you. 



It may here be proper to remark that the nature of this pen- 

 dulum is by no means new; it is of the gridiron kind, and al- 

 though extremely unlike it in outward appearance, is only a 

 new fpecies of that genus. Without further introdu6tion, I 

 ^will now proceed to give a brief defcription, with reference 

 to the accompanying (ketches, and then conclude with a few 

 general remarks. 



Fig. 1. and 2, Plate XIII. drawn to a fcale of one eighth of 

 the real dimenfjons, exhibit the fliape of the whole inftrument, 

 in which the parts of aftion being completely concealed from 

 view, it appears, excepting the ufual fufpenfion fpring, to h^ 

 made of folid brafs. The firfl: of thefe figures gives a front 

 view, the latter fhevvs it as feen edge wife. This figure of the 

 bob is ufed more on account of its being eafy to make, and 

 fightly, than from any other connderations; it is made of one 

 piece of brafs, about 7 inches diameter, 2,5 thick at the centre, 

 pnd weighs about 15 pounds avoirdupoife: the front and back 

 furfaces are fpherical, with a thick edge or cylindrical part be- 

 tween them. The apparent rod is a tube of brafs, fliewn in 

 both figures to reach from the bob nearly to the top; this con- 

 tains another tube and five wires in its belly, fo difpofed as to 

 produce altogether (like the nine-bar gridiron of Harrifon) 

 three expanfions of fieel downwards, and two of brafs up- 

 wards; whofe lengths being inverfely proportioned to their 

 dilatation, when properly combined, dellroy the whole ef- 

 fe6t that either metal would have fingly. The fmall vifible 

 part of the rod near the top, is a brafs tube, whofe ufe is to 

 cover the upper end of the middle wire, which is here fingle, 

 and otherwife unfupported. 



5 Reckoning 



