The hardening of both ends
should only be at the tips. The sliding center _I_ can be held in the
V-shaped groove by two light friction springs, as indicated at the
dotted lines _s s_, Fig. 115, or a flat plate of No. 24 or 25 sheet
brass of the size of _H_ can be employed, as shown at Figs. 116 and 117,
where _o_ represents the plate of No. 24 brass, _p p_ the small screws
attaching the plate _o_ to _H_, and _k_ a clamping screw to fasten _I_
in position. It will be found that the two light springs _s s_, Fig. 115
will be the most satisfactory. The wire legs, shown at _L_, will aid in
making the device set steady. The pillar _E_ is provided with the same
slides and other parts as described and illustrated as attached to _D_.
The position of the pillars _D_ and _E_ are indicated at Fig. 110.
[Illustration: Fig. 117]
[Illustration: Fig. 118]
We will next tell how to flatten _F_ to keep _H_ exactly vertical. To
aid in explanation, we will show (enlarged) at Fig. 118 the bar _F_
shown in Fig.
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