OPTICAL INSTRUMENTS. 



187 



proper position, in a strong light, and the lines traced as 

 above, when a correct likeness may be obtained by persons 

 unacquainted with drawing. 



Price, 12 inches long, $3.50. 

 " 18 " $6.00. 



A simple camera obscura may be constructed in the fol- 

 lowing manner : fix a convex lens, from one to three inches 

 diameter, in the hole of a window shutter, and if no light 

 enters the room but through the glass, the pictures of all 

 objects on the outside may be seen in an inverted position 

 on a sheet of white paper placed at the focus of the glass, 

 or at such a distance from it as they may be represented 

 clear and distinct. Price, 25 cts. to 75 cts. 



Draughtsman's Came- 

 ra Obscura and Cosmo- 

 rama. (Fig. 703.) 

 This convenient arrange- 

 ment of the camera when 

 set up is twenty-one 

 inches high, the sides 

 are hinged, and when 

 not in use, may, together 

 with the other parts, be 

 folded down into the 

 case ; the usual size be- 

 ing eighteen inches long, 

 fourteen inches wide, and 

 seven and a half inches 

 deep ; the larger size 

 being twenty-four inches 

 long, and of proportional dimensions. The lens and mirror, 

 the latter inclined at an angle of 45 degrees, are contained 

 in a box on the top of the case, which may be turned around 

 and directed to any part of the horizon ; also having a slid- 

 ing motion for adjusting the focus. The object is received 

 by the lens, and reflected by the mirror to a sheet of white 

 paper placed on the bottom of the box. One side of the 

 box is cut to admit the head and arms of the person who 

 desires to trace with a pencil the objects delineated. This 

 instrument also forms an excellent cosmorama, by placing 



