CH. VIII] 



PREPARATION OF LANTERN SLIDES 



328. Negatives as lantern slides. Many objects appear 

 equally well and equally clearly when projected from a negative as 

 from a positive or transparency. That is, there will be white lines 

 and white letters, etc., on a black background. This was a 

 favorite method of illustrating in the older works on physics and 

 projection. For examples, look at the pictures in Dolbear's Art of 



FIG. 1 1 8. PHOTOGRAPHIC CAMERA UPON A BASEBOARD HINGED TO A 



TABLE. 

 (From The Microscope). 



This is one of the copying, enlarging and reducing cameras. The objective 

 may be at the end, in a cone, or in the middle segment. For lantern-slide 

 making it is in the middle segment and the negative at the end, the whole 

 camera being directed upward toward the sky. 



By reversing the position of the camera, and placing the hinged board in a 

 vertical position, objects in liquids and any object in a horizontal position can 

 be photographed. 



NOTE. The arrangement shown in fig. 1 18 with a baseboard hinged to the 

 table, and with a camera which could be placed pointing upward or downward 

 was devised by the senior author in 1878 especially for photographing objects 

 in liquids or objects which must remain in an inclined or horizontal position. 

 The baseboard carrying the camera can be fixed in any position from the 

 horizontal to the vertical. (Proc. Amer. Assoc. Adv. Sc. Vol. XXVIII (1879), 

 p. 489; Science, Vol. Ill, p. 443, and Vol. IV, p. 5 (1884). 



