144 



Transactions of the Society. 



There are several of these solar projection Microscopes, by 

 various makers, in the Society's cabinet. Fig. 29 illustrates 

 Watkins' projection apparatus, which is very similar to that of 

 Cuff's ; the cat-gut and pulley are replaced by a rack-and-pinion. 

 The instrument is shown fixed to the pillar and tripod ; it has been 

 so placed for the purpose of being photographed for illustration, but 

 in actual use the square silver plate would be fixed to a window 

 shutter, the mirror being outside the window. The pillar and 

 tripod-foot would be removed from the limb, the screw-pin having 

 a butterfly-nut for this purpose ; the limb is held by a clamp on 

 the tube, which screws into the square plate. This tube has three 



Fig. 29. 



draws — they are not fully extended in the figure ; at the square 

 plate end of the tube there is an equi-convex lens, 11 in. in focus, 

 to condense the sunlight upon the object. The two butterfly-nuts, 

 on the front of the square plate, are for the purpose of attaching it 

 to the window shutter, and the milled head actuates rack-work for 

 rotating the mirror. It seems a wonder that, in the absence of any 

 heat absorber, the specimen upon the stage was not burnt up by 

 the condenser: it is probable that the sun's image had to be 

 placed considerably out of focus. 



To sum up the important points in this beautiful Microscope of 

 Watkins, we find that they are three in number; the first, and 



