632 PKOCEEDINGS OF THE AMERICAN ACADEMY. 



wax, blown upward, fell in drops and spatters on the upper surface of 

 the wax plate, rendering it unfit for accurate reconstruction work, 

 and there was the same disadvantage as before, that the cutting had 

 to be so done as to leave the saw-carf with its melted wax always 

 on the side of the wire away from the operator. These difficulties 

 were finally overcome by substituting suction for blast, and by caus- 

 ing the wire to emerge from the centre of the blowpipe hole, as 

 will be explained directly. 



As at present arranged, the apparatus consists of a sewing machine 

 (Wheeler ^K: Wilson), in which only a few changes have been required. 



These changes consist in the removal of certain superfluous parts, 

 such as the presser-foot, the bobbin and bobbin-holder, etc., and the 

 substitution for the needle and needle-bar of an arrangement for 

 holding the heated wire. 



The needle-bar is replaced by a cylindrical steel bar of precisely the 

 same diameter as the original needle-bar. This new bar may for con- 

 venience be called "needle-bar" (B, B, Figure n). It is thrice bent 

 at right angles, thus giving four regions, or arms, — two vertical and 

 two horizontal. The first of the two vertical arms is inserted, in place 

 of the original needle-bar, into the bearings of the head (H), and fastened 

 by a binding-screw to a block which in turn is connected to the lever (V) 

 by means of the link (L). The upper horizontal arm of the bar is 

 made about as long (20 cm.) as half the diameter of the largest wax 

 plate which it is designed to cut. The bending is such that this arm 

 and the two vertical arms are in one plane ; the fourth (lower horizontal) 

 arm is bent out of that plane, its free end being nearer the operator 

 than the corresponding end of the upper horizontal arm. A vertical 

 slit in the free end of the lower arm receives a copper wire, which is held 

 firmly by a binding-screw and terminates in a hook, as seen in Figure 3. 

 The lower end of the electrically heated wire (W), which is platinum, 

 is made into a loop that can be slipped on to this hook. The loop at 

 the upper end of the platinum wire is likewise made to slip on to a hook 

 at the lower end of a brass wire, which is supported indirectly by the 

 first vertical arm of the bent steel rod, or "needle-bar." Apart of 

 the brass wire is bent into a spiral spring (S), which serves to keep taut 

 the heated wire (W), the lower end of the brass wire being free to move 

 up and down through a hole in the lower of the two short horizontal 

 S({uare bars of indurated fibre which support it. These two bars are 

 clamped by binding-screws to a short vertical steel rod, which is in turn 

 attached to the first vertical arm of the " needle-bar " by means of two 

 scpiare rods of brass, bored at each end to receive the steel rods, and 

 furnished with set-screws. The whole of the apparatus thus far de- 



