THE SOLAR MICROSCOPE. 



An opening being provided in a convenient position in one of 

 the window- shutters, corresponding in magnitude with the aper- 

 ture in the board AA BB, the latter is screwed upon the window- 

 shutter, so that the two openings shall coincide. The mirror M 

 will then be outside the window-shutter, while the instrument 

 and its appendages wall be inside. The window selected should, 

 of course, be one having such an exposure that the sun's rays 

 can be reflected by the mirror in the direction of the axis of 

 the tube. 



12. To adjust the instrument, remove the piece x, which sup- 

 ports the slider, so that the light may pass unobstructed to the 

 amplifying lens. By varying the position of the reflector M, by 

 means of the milled heads c c', a position will be found in which 

 a uniformly illuminated disc will appear on the screen ; this disc 

 may be rendered more clear and distinct by adjusting the in- 

 strument by means of the rack and pinion attached to the tube. 



When these preliminary adjustments are made, the piece N is 

 replaced, and an object inserted in it ; the instrument being then 

 more exactly focussed, a distinct image of the object, upon a large 

 scale, will be seen on the screen. 



The management of the instrument will vary with the nature of 

 the object. If it be a very transparent one, a strong light thrown 

 upon it would cause it almost to disappear. The light, therefore, 

 in such case, must be so regulated as to produce the image in the 

 most favourable manner, which may always easily be accomplished 

 by moving the tube T' in and out of the tube T, until the desired 

 result is obtained. 



When the experiments are continued for any considerable 

 interval, it will be necessary, from time to time, to accommodate 

 the reflector M to the shifting position of the sun, which may 

 always be done by the milled-heads c c'. This adjustment, how- 

 ever, might be superseded by mounting the mirror 31 upon an 

 apparatus called a Heliostat, the effect of which is, to make the 

 mirror move with the sun, by means of clock-work. Such an appa- 

 ratus, however, is expensive, and the adjustment above described 

 is attended with no great inconvenience or difficulty. 



13. The substitution of the oxy-hydrogen, or electric light, for 

 the sun in this most instructive instrument, renders those who 

 use it, however, altogether independent of the sthi, so that it can 

 be used for a night as well as a day exhibition. Since the method 

 of applying to it the electric light has been already described very 

 fully in our Tract upon the Magic Lantern, the explanation need 

 not be reproduced here. 



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