310 Annual Report on the U. S. Coast Survey. 
The lever and level of contact first used, I believe, in the ad- 
justment of standard measures by Bessel, was applied to indicate 
the lengths of the bars. The levels were so delicate, that sev- 
- eral divisions upon them made up a quantity entirely insignificant 
in the measurement. The doubt which I had was, whether the 
sensibility of the apparatus had not been carried too far. This 
was, however, entirely removed, upon finding the rapidity and — 
certainty with which it could be used. The contact of two ad- 
jacent measures was between a blunt knife edge and a plane 
of agate. 
“The trussed support for the bars adapted to bearing the ap- 
paratus at two points only, and the tin covering or tube which sur- 
rounded the whole, were similar in principle to those used by Mr. 
Borden, but differed entirely in the adaptation of them; the bars 
moved freely on the trussed frame upon rollers, and were not 
attached to the covering tube in which the trussed frame itself 
was merely supported. 'The tin covering was conical and was 
doubled.” 
“The trestles admitted of the various motions required in 
placing the apparatus. The length of the whole, about twenty 
feet, (six metres,) gave a weight which permitted easy and rapid 
transfer by four men, when covered with several thicknesses of 
imperfectly conducting material to keep the fluctuations of tem- 
perature within moderate limits. In arranging so many and va- 
rious details, it is not to be expected that some of them will not 
admit of improvement; but the performance of the apparatus 
was highly satisfactory, working with a rapidity and accuracy 
quite beyond my most sanguine expectations, and making com- 
paratively light the labor of all concerned in the excitement pro- 
duced by expectations constantly surpassed. The contacts were 
usually made in much less time than the setting of the forward 
trestles for the next measure. The following statistics — 
of nearly seven miles was completed in seventeen working days; 
not reckoning the time lost by bad weather, or occupied by 
change of camp, and by comparisons of apparatus. The length 
of the apparatus was compared before and after final measure 
ment with a standard iron bar, with which it had been compared 
in the office, by using Mr. Saxton’s reflecting pyrometer.” 
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