«226 AN ACCOUNT OF THE 
have coffers and stands made for it. But the employment of the chain in 
this way would have evidently consumed an immense period of time, not only 
in the operation itself, but still more, in the preparation of the coffers and 
stands, the latter requiring to be made with elevating screws.. This alone 
was a sufficient objection; even supposing the great delay it would have 
caused, none. For in this remote part of the country one such stand 
could not be properly executed, if at all, without incredible difficulty.. 
What then would have been the case when there were twelve or fourteen 
to be constructed. To this must be added the consideration, that I was 
alone in a work which requires at least two to execute it properly... From 
the beginning therefore I relinquished the idea of employing the chain— 
except as a standard of comparison, for which purpose it was invaluable. 
2. Wuen I had rejected the chain it appeared that the best substitute 
would be a set of rods constructed of pine wood; the comparative unalter- 
ability of which has been long known. Such rods have been employed by 
some philosophers in the measurement of a degree, particularly by La 
Carnie and General Roy. It is true that General Roy rejected the 
measurement made with them, in consequence of the changes which he 
_ found the greater or less quantity of moisture im the atmosphere produced 
in their length, yet when we look at the small error which a re-measurement 
of this base with glass rods detected, we shall be satisfied that for the pur- 
pose I contemplated, pine rods are capable of sufficient accuracy. He 
found the difference between the two measurements only two feet, and this 
in a distance of 5; miles, and I certainly thought so small an error as this, 
could never be alleged as an objection to the success of my operation. 
