Meafurement of a Bafe on Hounflow-Heath. 419 
The operation with the chain was fufpended during the 1 8th 
and 19th of June, thofe days having been employed in fettling 
certain matters with Mr. Ramsden relative to the deal rods, 
as well as to give time for the making of a holdfaft for the 
rear end of the chain, invented by Lieut, Colonel Pringle. 
This machine, whereof the plan at large is reprefented by 
dotted lines at the handle of the chain, as it is in fmall 
by the two elevations adjoining in tab. XVII. confifts of a 
femi-circular iron plate, from the bottom of which projects 
two double and one fingie prong. In the middle, between the 
two double prongs, a fe mi- circular cavity is formed, fitted to 
receive the heel arrow on one fide, while that in the brafs re- 
ceives it on the other. In a locket in the middle, a ftrong 
wooden handle, refembling that of a fpade, is placed. Thus 
the rear handle of the chain being applied to the arrow, the 
holdfaft embraces with its double prongs the ftraight part of 
the brafs, and in that pofition, being forced into the ground by 
the acftion of a man at the handle, the rear end of the chain is 
thereby kept fo firm as to be immoveable by the efforts of the 
two men at the other end, in ftretching.it to its true pofition, 
for the front arrow. 
On Monday, the 21ft of June, the operations were refumed, 
by meafuring twice with the chain (forwards and again back- 
wards) the thirteen hypothenufes comprehended in the fecond 
fection of the bafe, between Hanworth Summer houfe and 
the north-weft bank of the great road (an old Roman way) 
leading from Staines to London. This being the fmootheft* 
part of the Heath, and the holdfaft being now applied, the 
two meafurements differed only one inch and a half in the 
diftance of 7800 feet. This inftarice of accuracy is alone fuf- 
fxcient 
