Menfuremcnt of a Bafe on Honnflow-Her.th. 41 « 



The operation with the chain was fulpended during the i8th 

 and 19th of June, thole days having been employed in lettllrjg 

 certain matters with Mr. Ramsden relative to the deal rods, 

 as well as to give time for the m.aking of a holdfait for the 

 rear end of th.e chain, invented by i^ieut. Colonel Pringls. 

 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 elev.itions adjoining in tab. XVII. confifts of a 

 femi-circular iron plate, from the bottom of which projc6ls 

 two double and one lingle prong. In the middle, between the 

 two double prongs, a femi-circular cavity is formed, fitted to 

 receive the fteel arrow on one fide, while that in the brafs re- 

 ceives it on the other. In a focket 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 

 hoidfaft embraces with its double prongs the ftraight part of 

 the brafs, and in that pofition, being forced into the ground by 

 the a6llon 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 2iil: 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 hoidfaft being now applied, the 

 two meafurements differed only one inch and a half in the 

 diftance of 7800 feet. This inftauce of accuracy is alone fuf- 



ficient 



