very delicate knife
edges, sometimes of agate, sometimes of hardened steel, and these knife
edges rest, when in use, on a block of agate or steel, so that there is
a minimum amount of friction. When not in use the balance beam and knife
edges are lifted from the block and held firmly by a metal arm, or else,
as is the case with some balances, the post supporting the block is
lowered, leaving the beam and knife edges out of contact with it. The
object of this separation is to prevent any rough contact between the
knife edges and the block on which they rest. Advantage should always be
taken of this device whenever any fairly heavy load is put on or taken
off of either pan, as the sudden tipping of the beam might chip the
knife edges if not supported. When the load is nearly balanced there may
be no harm in carefully adding or removing small weights while the knife
edges are resting on the block, but even then it is safer to lower the
beam and pans. It should be needless to state that as level and rigid a
support should be had for one's balance as circumstances permit.

METHOD OF USE OF BALANCES. Before using a balance one should see that
the pans are clean, that the base of the balance is properly leveled
(the better balances have a spirit level attached) and that the pans
balance each other without load. When slightly out of balance the
defect may be adjusted by _unscrewing_ the little adjusting nut at the
end of the beam that is too light, or by _screwing in_ the nut at the
opposite end. Having seen that the adjustment is perfect the pans should
be lowered and the object to be weighed placed on the _left-hand pan_
(because a right-handed person will find it handier to handle his
weights on the right-hand pan). One should next guess as nearly as
possible the weight of the stone and place well back on the right-hand
pan the weight that he thinks comes nearest to that of the stone. If the
weight is too heavy the next lighter weight should replace it. Smaller
weights should be added until a perfect balance is had, the small
weights being neatly arranged in the order of their size, in order to
more rapidly count them when the stone is balanced. This is the case
when the pointer swings approximately equal distances to the right and
to the left and there is then no need to wait for it to come to rest in
the center.

It is well to count the weights as they lie on the pan (which is easily
done if they have been arranged in des