THE construction of a small stereop- 

 ticon for use in the home or lecture 

 room is an easy task for the work- 

 man who possesses the usual tools, such 

 as a hacksaw, small drill-press, taps, 

 dies, etc. The design presented here- 

 with is one well adapted to amateur 

 construction, and in the finished instru- 

 ment the builder will have one which 

 incorporates, in a simplified manner, 

 everything which makes for comfort and 

 efficiency in operation. At the same 

 time, it will cost little to build if the 

 objective and condenser are purchased 

 second hand. 



From the illustrations, the reader will 

 note that the finished instrument is of 

 the conventional form with one or two 

 exceptions. The usual bellows is sup- 

 planted by telescoping c\lindcrs of metal ; 

 the bellows is difficult to con- 

 struct and, when made, it is no 

 more effective than the de\ice 

 shown in the drawing. The 

 con\entional lamp-hood of sheet 

 metal has been supplanted b\- an 

 earthern hood made from a 

 flower-pot; this construction 

 permits the use of a simpK- 

 made arc-lamp without gears or 

 worms and, furthermore, it pre- 

 \ents the heat of the arc fron) 

 attacking the lamp parts. The 

 heat is dissipated through an 

 opening in the top, above the arc, and 

 the condensing lens is protected by a 

 ilisk of thin glass loosely clamped to the 

 tront of the flower-pot hood. Every 

 detail of the instrument and dimensions 

 is shown in the drawings; it is therefore 



Fig. 1. 

 conde 



unnecessary to repeat dimensions in the 

 text of this article. Before starting the 

 work, the builder should purchase the 

 condensing lens, the objectixe and a 

 slide carrier of the conventional sort. 

 The condenser will cost, mounted as 

 shown in Fig. I , about $2. The objectixe. 

 Fig. 2 A, will cost from $3 to $10, 

 depending upon its quality-, focal length, 

 and condition, if second hand. The 

 slide carrier of the sort shown in Fig. 3 

 costs about $5. 



The focus of the objectixe will have an 

 important bearing upon the length of 

 the cylinders, C and D, Fig. 2, and the 

 dimensions given are for a lens of lo-in. 

 focus. This is an excellent size, as it 

 throws a picture approximately 6 ft. 

 square at a distance of 20 ft. from the 

 screen. If the instrument is to be used 

 in a smaller room, the objecti\"e 

 should be of shorter focus. These 

 oVjjective lenses are usually sup- 

 plied in a mounting, with a 

 flange and a knurled adjusting 

 knob, which actuates a rack and 

 pinion arrangement. The follow- 

 ing table shows the sizes of pic- 

 tures projected b\- lenses of vary- 

 ing focuses at \arious distances. 

 l"or example : With a lens having 

 an equivalent focus of 7 in., a 

 picture 6.5 ft. square would be 

 projected if the machine were 

 15 ft. from the screen; 8.5 ft. square 

 at 20 ft., etc. 



The table is prepared as an aid to 

 careful selection of a lens suitable to the 

 room in which the stereopticon views 

 are to be exhibited. 



767 



