138 OPTICAL PROJECTION 



the glass slides alone are carried in a grooved box, and used 

 in some form of frame or ' carrier,' inserted in the slide- stage 

 of each lantern. Of these carriers there are many kinds. 



The simplest is a solid frame, with a grooved opening into 

 which the slide drops from the top. This kind of carrier has 

 to be withdrawn from the lantern every time a slide is changed, 

 inverted to drop the old slide out, and then re-inserted with 

 the fresh one. About this there is some risk, and these 

 carriers are gone out of use since better ones have been 

 made. 



Another form, more used some years ago than now, is 

 known as the panoramic carrier. In this the wooden frame is 

 the exact length of three common slides, and is clear from 

 end to end, but has only one mask or opening in the middle, 



FIG. 73. Beard's Self-centering Carrier 



of the proper size. The carrier is left in the lantern, the more 

 firmly fixed the better, and the slides are slid in, so that when 

 a second slide is pushed in after the first, exactly even with 

 the end of the carrier, the first or middle one is in place. A 

 third is pushed in similarly ; and after that, as a fresh slide 

 is pushed in, care must be taken to catch the slide which is 

 simultaneously pushed out. The chance of forgetting this is 

 a risk about the panoramic form of carrier, which also has 

 the great drawback of requiring both hands at the instant of 

 changing. By having one end of the panoramic carrier cut 

 into stops at different distances from the end, different sizes 

 can be used after each other and still be centered. On rare 



