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DESCRIPTION OF PLATE IV. 
The chain used in measuring the bases is one hundred feet long, 
consisting of twenty links of hard round iron, one quarter of an 
inch in diameter, which are simply hooked together by folding 
down the extremities of the bar, and pinning them to the body, as 
represented in Fig. I. PP. 
Fig. 2. Represents the handles or extreme links, with the termi- 
nating point marked by a line AB drawn on a square piece of 
brass affixed to the link, and having also a notch B into which the 
pin Fig. 5 could be placed upon occasions when great accuracy 
was not required. 
Fig. 3. The mark for each length of the chain, being a square 
plate of brass, with four spikes or prongs beneath to hold it firm 
on timber, ice, or on the ground, with a moveable piece C, which 
slides along a groove, so as to coincide with the terminating line 
AB in Fig. 2. 
Fig. 4. A staple or grape to be pushed down into the’ ground 
over the handle, Fig. 2. to keep the chain steady while the adjust- 
ment is made. 
M2 
