190 



BENJ. PIKE S, JR., DESCRIPTIVE CATALOGUE. 



To use, fix the 

 instrument to the 

 table by the screw, 

 with the stem in- 

 clined. Place a sheet 

 of paper under the 

 prism, which must be 

 turned, so that the face 

 may be exactly oppo- 

 site the object to be 

 drawn ; by looking 

 through the eye-hole 

 downward on the pa- 

 per a picture of the 

 object will be seen. 

 The proper position of 

 the eye-hole is of the 

 first importance in the 

 use of the instrument ; 

 if the aperture is too 

 far over the prism, the 

 pencil will be indis- 

 tinct, and if not far 

 enough the object can- 

 not be seen sufficiently 

 clear ; a little practice 

 will make this perfectly easy. In first attempting to use 

 this instrument many persons lose sight of the pencil, 

 merely by the motion of the head in breathing, which they 

 are not aware of. The longer the stem is drawn out, the 

 larger the object will appear, and the view less extended. 

 If the object to be drawn is two feet from the prism, and 

 the paper one foot, the copy will be half the size of the 

 original ; if the object is one foot from the prism and the 

 paper two feet, the copy will be twice the size ; and so in 

 proportion for any intermediate distance. 



Price, 18.00 to $12.00. 



Graphic Mirror. (Fig. 707, next page.) An instrument 

 for drawing objects in true perspective, and for copying, 

 reducing, or enlarging other drawings. The upper part of 

 the instrument consists of a triangular box, having a fixed 

 reflecting mirror or looking-glass within it, and a transparent 



