142 THE HISTORY AND DEVELOPMENT OF THE MICROSCOPE 



this microscope are twenty-four in number; they vary in focal 

 length from lour inches to one-tenth of an inch; ten of them are 

 supplied \vith Lieberkiihns. A small arm, capable of carrying single 

 lenses, can lie applied at T, and when turned over the stage the in- 

 strument becomes a single microscope ; there are four lenses suitable 

 for this purpose, their focal length varying from y^th to T Lth of an 

 inch. The performance of all the lenses is excellent, and no pains 

 appear to have been spared in their construction. There are 

 numerous other pieces of accessory apparatus, all remarkable for the 

 beauty of their workmanship.' ' 



I'.nij. Martin not only in this way greatly advanced the 



;-hanical arrangements of the microscope, but he improved the 



optical part. He used a Huvgheniaii eye-piece on the telescope 

 formula, where the focus of the eye-lens was that of the field-lens 

 :!. and the distance between them 2; but instead of employing a 

 -inu'le eve-lens he bi-oke it up into tw T o of equal foci, that nearest the 

 eye being a crossed ' lens, and the other a plano-convex, the steeper 

 convex it ies ( >f t hese lenses being towards each other. In addition to this 

 he placed at a short distance above the nose piece an equi-convex lens 

 of 5^ inches focus ; this acted as a back lens to all the objectives. 

 so that when an objective was changed it was really only the front 

 lens of a compound objective that was altered. 



Cuff designed and made a microscope, in 1744, which Baker 

 figured and described in his ' Employment for the Microscope ' in 

 1753, which possessed several conveniences and improvements. Xot 

 the least of these is that which gives greater delicacy to the fine ad- 

 justment than is found in any preceding model. It was subse- 

 quently further improved by the addition of a cradle joint at the 

 bottom of the pillar by Adams. Cuff also designed a simple form of 

 micrometer. 



There \\ere three designs of microscopes by George Adams, of 

 London, in 1 7 M> and 1771. \\hich have many points of interest, but 

 scarcely contribute enough of distinctive improvement to the modern 

 forms of the microscope to detain us long. That designed in 1771 is 

 figured in the Adams M icmgrapliia Illustrata,' and is reproduced 

 in fig. 111. 



In this Lnstrumenl Adams claims to have embodied a number of 

 improvements on all previous constructions. He applied "two eve- 

 glasses at A, a third near 15, and a fourth in the conical part between 

 B and C,' by uhich he increased 'the Held of view and of light ;' 

 draw-tub. -s were at A and I'., by which these lenses could be separated 

 more or Less, but the probability is very great that these were 

 .-imply copied from the improvements of a like kind devised by B. 

 Martin and described above. He also arranged the object-lenses, or 

 buttons,' " and /. to be combined ; seven ' buttons ' were provided, 

 erspecula |' Lieberkiilms'j highly polished, each having 



ignitiei- adapted to the focus of its concavity, one of which is 

 and the 'buttons' could also be used with 'any 

 our of these specula ' by means of t lie adapter. //. 



- 1 /-"'-"-" /". :'.nl.''. 1. London, 1H55 8vo 



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