Earty History of the Microscope. 7 



all the draw tubes were closed the length from eye-piece to 

 objective is 36'5 centimetres, or 14 in. when all were drawn out 

 as far as the marks I, II, III, IV ; the total length is 41, 49, 54, 

 56-5 cm. respectively, or, expressed in English inches, 16 in., 

 19J in., 21i in., and 22^^ in. The body of the instrument is of 

 cardboard, covered with parchment coloured green and gilded ; the 

 largest tube has a diameter of 8 cin. or 3^ in., and the lowest 

 tube carries on its lower half a broad spiral band of cardboard, 

 also covered with parchment, which gears into a spiral cut in the 

 cardboard cylinder, round which is the brass band bearing the 

 inscription ; the three brass legs are 15 cm. or 5j^ in. long. 

 The objective, a biconvex lens, is held in position at the bottom 

 of the screw tube by a screwed cap, and the object is focused by 

 turning the object-holder up or down by means of the screw on 

 this tube, which is 2^^ in. long, and 1 in. in diameter. The eye- 

 piece is missing, and the field lens is a large somewhat yellow 

 biconvex one, 6 cm. or 2^ in. in diameter, and 5 mm. or a in. 

 thick. These measurements agree practically with those of the 

 instrument I mentioned above, except the tube is not as large as 

 a man's thigh ; this, I think, must be an exaggeration. 



The microscope described by Philip Bonani fifty years later 

 was, as far as the lenses were concerned, similar in construction 

 to the foregoing, consisting of an object-glass, a middle or field- 

 glass, and an eye-lens ; but the form of mounting was different, 

 in that he placed the body in a horizontal position. It was 

 also provided with a stage for the object, and with a coarse and 

 fine adjustment for the body ; the former was rack and pinion, 

 and the latter was effected by a screw on the body at the objec- 

 tive end, and finding, doubtless, that the weight of the body, 

 especially when the fine adjustment was back, made his in- 

 strument somewhat unsteady, he introduced a triangular sup- 

 port near the eye-piece, in which, of course, the body could be 

 easily moved backwards and forwards in obedience to his fine 

 adjustment screw. Bonani seems to have worked with direct 

 light, and between the lamp and the stage he placed a short 

 tube containing two double convex lenses ; in fact, he intro- 

 duced a substage condenser. This instrument was, to my 

 mind, at any rate so far as the mechanical part went, a very 

 long step in the direction of improvement. 



We find no further record of any importance from this time 

 till 1702, when Jean Zahn published a work at Nuremberg, 

 describing, amongst many others, two binocular microscopes, and 

 also a figure of one by Francis Grindelius, used for opaque 

 objects ; its optical parts consisted of six plano-convex lenses, 

 placed as shown in the drawing, but lie gives no record of its 

 size. And in the same year, Mr. John Marshall brought out 

 his microscope, which, however, from its unwieldy nature, was 



