Meafurement of a Safe on Houn fio W- Heath , 397 
exactly of the fame length, fubdituted in their head, with 
femi-circular holes (as reprefented in the Plate by dotted lines 
near the joint of the handle) to receive the heel arrows, then 
to be made ufe of in the manner already mentioned. 
This mod; excellent chain feems not to have buffered any 
perceptible extension from the ufe that has hitherto been made 
of it. It is fo accurately condrudled, that when dretched out 
on the ground, as in common ufe, all the long plates lying 
vertically or edge-wife, if a perfon, laying hold of either end 
with both hands, gives it a flip or jerk, the motion is, in a 
few feconds, communicated to the other end, in a beautiful 
vertical ferpentine line ; when the perfon, holding that handle, 
receives a fudden fhock, by the weight of the chain pulling 
him forcibly. The chain weighs about eighteen pounds, and 
when folded up is eafily contained in a deal box, about four- 
teen inches long, eight inches broad, and the fame in depth. 
Deal Rods „ Tab. XVIII. 
The bafes which have hitherto been meafured in different 
countries, with the greateft appearance of care and exadhiefs, 
have all, or for the mod: part, been done with deal rods of one 
kind or other, whofe lengths being originally afeertained by 
means of fome metal dandard, were, in the fubfequent appli- 
cations of them, corredted by the fame dandard. Having thus 
had fo many precedents, ferving as examples to guide us in our 
choice, it was natural enough that we fhould purfue the fame 
method in the meafurement to be executed on Hounflow- 
Heath ; taking, however, all imaginable care, that our rods 
Ihould be made of the very bed materials that could be pro- 
cured; 
