2q6 M^jor-General Roy*s Account of the 



firfl: mode of application it was fooii difcovered, as we fliall 

 have occalioQ to mention hereafter, how admirably the chain 

 performed ; and that, with fome farther precautions, a ftill' 

 greater degree of exactnefs might be attained, by fupporting it 

 on ftands, or even on planks, laid on, or but little removed 

 from, the common furface of the earth. For this purpofe, 

 the two end-links were altered, each being now miade equal to 

 one foot, exclufive of the handles. By referring to tab, 

 XVII. the nature of this alteration will be eafily conceived. It 

 confifted in fcrewing to the under fide of the handles, very 

 near the joints, two feather- edged pieces of brafs * ; the one 

 denoting zero, and the other loo feet. Over the dart at the 

 iirft, a plummet with a fine lilver wire being fufpended, that 

 wire, by a very fimple apparatus, hereafter to be defcribed, 

 may be brought accurately to coincide with any point whatever 

 of commencement: and at the fe.:ond, a fine line with a 

 knife, or other fliarp inftrument, being drawn on a piece of 

 card placed there for the purpofe, and changed as often as 

 needful ; or, as was likewife pradifed, and found to anfwer 

 better, a line on a moveable (lide of brafs, attached to the top 

 of the fland or plank, being brought to coincide with the fea- 

 ther-edge, and then faftened underneath ; the extremity of the 

 100 feet is readily afcertained : and thus the meafurement 

 may be continued on with great accuracy to any diftance at 

 pleafure. 



That the chain, in this its altered ftate, may flill be advan- 

 tageoufly applied to ordinary meafurSment on the furface of. 

 the earth, the pieces above defcribed, having fteady pins, and 

 being faftened with fcrews, can be eaiily removed, and others, 



* They w^jre originaUy of, hrafs, but are now of fteel, that tlve edges by being 

 harder, might run lefs rifk of being damaged. 



7 cxadly 



