Oil' DENISON tJNtVERStxy. g 



which serves the purpose of a holder for the wax sheets. The magni- 

 fication being determined upon, the wax sheets are cast with a corres- 

 ponding thickness. The screen is placed at the proper distance as in- 

 dicated by the scale, the images on the slides are projected in their ser- 

 ial order and the patterns traced on the wax sheets. 



In case much detail is required, the contrast may be increased by 

 covering the wax surfaces with thin white paper, and then tracing with 

 a pencil, the pressure of the point being sufficient to transfer the out- 

 line to the wax beneath. 



The advantages of this method are at once evident. In the first 

 place it is labor saving. An entire series may be patterned within 

 the space of an hour or two. Large models may be constructed with- 

 out the extremely tedious process of moving the wax sheet while trac- 

 ing, as is necessary with the camera lucida. And also, almost absolute 

 accuracy is insured, which by the usual method is difficult to obtain, 

 owing to the obscure field and possible lateral distortion of the camera 

 lucida. It is only necessary to use an objective which will include all 

 the field desired as the magnification depends upon the distance of the 

 sheet from the lantern. 



Cutting out Sectional Drawings. After the sections have been out- 

 lined on the wax sheets, they are to be cut out in serial order. This 

 may be done, either with an ordinary pen knife, or better still, with an 

 apparatus designed especially for this purpose. It consists of a wooden 

 frame, between the two free ends of which a fine piano wire is 

 stretched. I'he tension of the wire is varied by a thumb screw. A 

 platform is attached to the lower arm, the wire being passed through a 

 perforation in the center. As shown in Fig. i. 



When in use the apparatus is clamped to a table. The cutting is 

 accomplished by simple pressure of the wax sheet against the wire. 

 The smallest piano wire, with a diameter of from .037 to .035 of an 

 inch, should be used. Experiments in heating the wire by electricity 

 have so far proven unsatisfactory. For when the heat is increased to 

 the proper degree, fusion of the cut edges takes place. All the sec- 

 tions can be cut at once, and then built up, or if only a small quantity 

 of wax is available, the cutting and modeling may be carried on to- 

 gether section by section. Thus the waste may be used for casting 

 additional sheets. If the first method is followed it is well to number 

 the drawings to guard against any misplacement in the final recon- 

 struction. When the sections have been fitted, they are cemented to- 



