Megadiascope. 



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Projection of apparatus which are placed on the Optical Bench of the Megadiascope. 



Fig. 5. 



obliquely in an upward direction. If the inclination is considerable, the projection screen must naturally 

 be adjusted obliquely in the same proportion. 



The diapositives are contained in a change frame which slides in the two grooves above 

 and below the condenser. The change frame given with the megadiascope is the usual diapositive 

 size (9x10.5 cm. = 3.54x4.13 ins.). This is the usual size of the diapositives dealing with astronomy 

 meteorology, physical geography and physics, of which we have a special list which we shall be glad 

 to forward post free to all interested. Instead of the frame for size 9 x 10,5 cm. we can also supply 

 it size 8,5 x 10 cm. (the usual size of landscape views sold) or size 9 x 12 cm. without change of price. 



The images are focussed on the projection screen in a coarse manner by 

 sliding the objective carrier along the optical bench, and fine focussing is obtained by means of a knob 

 on the, objective. As to the method of obtaining maximum brilliancy of the images, reference should 

 be made to the first paragraph of this section. 



In place of the achromatic projection objective, a Steinheil group antiplanet, 

 a Voigtlander Heliar or a Zeiss Tessar of the same focus may be selected when great 

 importance is attached to obtaining an image which is equally as sharp at the edges as in the centre. 

 The objectives just mentioned are more efficient than the projection objective, but the cost is also 

 greater. 



We have included some rules for the manipulation of the arc lamp, on page 1217. 



2. Projection of apparatus which are placed on the Optical Bench of the Megadiascope. 



F i g. 5 shows the arrangement for this method of projection. The adjustable stage supplied 

 with the megadiascope is fixed to the optical bench: the apparatus to be projected being mounted 

 on this stage. The illustration indicates the method of setting up a Kolbe electrometer for projection. 

 In the same manner all the fine instruments can be projected which are arranged for objective pro- 

 jection and their number is steadily on the increase. We will only mention the wave-projecting machine. 

 Xewton's transparent colour discs, sectional model of steam cylinder, Andrew's press, the rotating 

 star chart, etc., etc. By means of the projection thermometer, the action during freezing, the mixture 

 of liquids, etc. can be very beautifully demonstrated. All phenomena which are capable of projection 

 at all can be projected by the megadiascope. 



C!. 4063. 



