1784 



Journal of Applied Microscopy 



250 mm. is given below and shows a range of possible magnifications with the 

 lens from j\ to 5. 



Having set the camera at the de- 

 sired length, the object is placed on the 

 floor beneath and the camera may then 

 be focused by sliding the frame up or 

 down in the supports. A direct move- 

 ment of the camera frame by the hand 

 is apt to be jerky or to make accurate 

 focusing difficult. To obviate this the 

 following device is used : Alongside 

 the camera frame (on the left) at a 

 distance of 5 cm. from it runs a vertical 

 wooden rod o to 4 cm. in diameter 

 (Fig. 1). This rod is pivoted at its 

 upper end to the ceiling near the first 

 pulley wheel and at its lower end is 

 pivoted on a wooden bracket which 

 extends from the wall just below the 

 board to which the iron base plate is 

 attached. The rod is thus within easy 

 reach of a person focusing the camera, 

 and turns freely. Its upper end for about 6 cm. is formed into a spool and 

 about it the rope running to the counterpoise makes one turn. The remainder 

 of the rod is octagonal. By turning the rod with the hand the camera may be 

 moved up or down with great delicacy, while the rod offers no hindrance to the 

 direct and more rapid movement of the camera by hand. If but one section of 

 the camera is in use care should be taken to change the counterpoise to cor- 

 respond. 



If the camera is conveniently situated the illumination of objects to be pho- 

 tographed is best accomplished by daylight or direct sunlight (see Fig. 7). We 

 are accustomed to use the arc light. For small objects the electric arc lamp and 

 condenser of the projection lantern with attached alum cell is made use of (as in 



Fig. 2. — Showing the apparatus in use with 

 an ordinary photographic lens, as when 

 making Fig. 7. 



