388 General Notes. [April, 
which in connection with a vernier, J, will read to tenths of these 
or one hundredth of the circumference, or, as a whole, to one 
ten-thousandth of an inch. Æ, or the head of the screw, extends 
through a hole in the glass box, so as to be turned by hand. To 
the right of the fulcrum, F, is a screw, e, on which a ball, D, 
works, and is for the purpose of adjusting the balance at mean 
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_ sea-level. When this is done the screw, G, is run in or out as the 
zase may be to measure the increase or decrease of the weight of 
ir. The screw, G, might be made to carry a vernier along the 
valance bar, c, to register the number of turns of the screw, but 
such is not shown in this sketch. O is a handle for carrying the box 
y mm are fulcrums on which a spring bow, o o, rests. 
