4 BULLETIN Of THE LA6ORATORIES 



In that case, the wax may be cast in shallow boxes, constructed from 

 heavy oiled paper. 



But in order to secure scientific accuracy, and usually this is de- 

 sirable if not essential, it is necessary to have the wax sheets of known 

 and exactly uniform thickness. In order to secure such sheets a cast- 

 ing box is necessary. A moulding box such as is used in the chalk 

 plate engraving or stereotyping process answers every purpose. Such 

 box may be improvized by using two perfectly smooth metal plates of 

 suitable size. Between these plates, and on three sides, are placed 

 narrow metal strips of the required thickness. The plates, having been 

 previously warmed and oiled, are clamped together and the melted wax 

 run in. The secret of obtaining good results lies in having the plates 

 at just the right temperature. If too cool, the chilled wax will have a 

 striated uneven surface. If too warm upon attempting to remove the 

 sheets the wax will be found adhering to the plates. Care must be 

 taken also to pour the wax in a steady stream, otherwise the sheet will 

 contain air bubbles. It is necessary, moreover, to oil the plates before 

 each casting. Vasehne is best suited for this purpose. 



Tracing. The patterns are traced on the wax sheets by the aid of 

 the camera lucida or the projection microscope. An ordinary lead- 

 pencil or a porcelain stylus is used for the purpose of tracing. The 

 latter is better followed by the eye on the dark wax background. 



It must be remembered that the optical principles involved in the 

 camera lucida require that the drawing surface shall be tilted toward 

 the microscope twice as many degrees as the mirror is depressed be- 

 low 45 degrees. Often when the magnification is high, or the object large, 

 it becomes necessary to move the section in the field, which in turn 

 necessitates a corresponding change in the position of the wax sheet. 

 This is not only a tedious process, but necessarily introduces errors and 

 is entirely obviated with the projection method. Often the desired 

 magnification requires sheets too thin to work with. Such an obstacle 

 may be met, if every other or every third section be drawn on sheets 

 twice or three times the estimated thickness. 



The latest development in wax modeling, as originated in our lab- 

 oratories, is the process of wax tracing by means of the microscopic 

 lantern projector. 



A small movable screen is used on which to project the sections. 

 By moving this screen in the focal plane, a graduated scale is made 

 out to indicate different magnifications. On the screen is a frame 



