110 



THE AMERICAN MONTHLY 

 MICROSCOPICAL APPARATUS. 



[April, 



Marshall's Compound Microscope, — This curious old 

 microscope was invented by John Marshall in the early part of 

 the eighteenth century. It was made and sold by him at the 

 Archimedes & Golden Spectacles in Ludgate street, London. 

 The figure accompanying, and also the de- 

 scription, is abstracted from Cantor's '''Lec- 

 tures on the Microscope.'''' The instrument 

 was first figured under the word microscope 

 in Harris's "■ Lexicon technicum " (1704). 

 Several improvements were em- 

 bodied in its construction. The 

 fine-adjustment screw was con- 

 nected with the sliding socket, 

 supporting the arm in which the 

 body screw fitted. This system 

 was a distinct mechanical im- 

 provement. The object could now 

 be viewed during the actual proc- 

 ess of focusing, as the image 

 would remain steadily in the field. 

 Hooke's arrangement for carrying 

 a rotating stage was modified into 

 a fork, and instead of being clamp- 

 ed on the base by a thumb-screw 

 it is here applied with a thumb- 

 screw clamp on the pillar itself. 

 Hooke's ball-and-socket joint is 

 here shifted to the lower end 

 of the pillar, 

 where it gives 

 amovementof 

 inclination to 

 the whole 

 body of the 

 m i c r o s CO p e 

 instead of to 

 the body tube 

 only, as in pre 

 vious instru- 

 ments. A con- 

 densing lens 



placed below the stage, on jointed arms, appears. From the 

 singular position of the candle beneath this condenser it is prob- 

 ab.e that up to this date (1704) the mirror was still unknown 

 as a microscopical accessory in England. 



Marshall's arrangement of the fish trough with the " Lead 

 Coffin, to be put on the fish to hinder it from springing away, 



