and bringing the crescent of sufficient depth that no possibility exists of the dart touching in or on the edges of it. We will now draw in the impulse roller and make it as light as possible consistent with strength. A hole is shown through the impulse roller to counterbalance the reduced weight at the crescent. When describing [Fig. 24], we gave instructions for finding the dimensions of crescent and position of guard pin for the single roller. We will find the length of horn; to do so we must closely follow directions given for [Fig. 25]. In locating the end of the horn, we must find the location of the center of the crescent and ruby pin after the edge of the crescent has passed the dart. From the point of intersection of
A′
b
with the safety roller we transfer the radius of the crescent on the periphery of the safety roller towards the side against the bank, then draw a line from
A′
through the point so found. At point of intersection of this line with the real impulse circle
r i r i
we draw an arc radiating from the pallet center; the end of the horn will be located on this arc. In our drawing the arc spoken of coincides with the dart radius
g g
. As before pointed out, we gave particulars when treating on [Fig. 25], therefore considered it unnecessary to further complicate the draft by the addition of all the constructional lines. We specified that the freedom between ruby pin and end of horn was to be 1½°; these lines (which we do not show) are drawn from the pallet center. Having located the end of the horn on the side standing against the bank, we place the dividers on it and on the point of intersection of