ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 299 



however, screwed together, but clamped and held together by a metal 

 ring. There were six of these objectives, of various magnifying powers. 



The object-stage carries, by sliding on, several devices for viewing 

 drops of blood, of water from infusions, and also the circulation of the 

 blood in small fishes' and tadpoles' tails. One of these devices is a 

 brass-bound glass tube, fixed by means of a spring inside the handle of 

 the Microscope ; the small fish being held in water in the tube with its 

 tail spread out on the glass stage-plate. 



Joblot calls this instrument in the text, " Troisieme et dernier 

 nouveau Microscope universelle," and used it principally for examina- 

 tion of the circulation of the blood in young fishes' tails, a subject which 

 had been discovered some years previously by the famous English 

 " Dr. Hervee " (as Joblot calls him), but not clearly demonstrated until 

 the advent of a suitable Microscope. He also used it for the examina- 

 tion of drops of water from infusions of various substances, such as hay, 

 leaves, wood, pepper, etc., as taught by Leeuwenhoek, and judging by 

 the figures in his book, Joblot must have seen most wondrous and 

 extraordinary creatures in these infusions : worms with snakes' heads, 

 Crustaceans with a human face on their back, Rotifers aud Infusoria of 

 fantastic shape — the species of which can only be vaguely guessed at. 

 In two places Joblot figures young dragons under his Microscope, or held 

 in forceps, unless indeed the engraver of his plates took liberties with 

 his drawings. 



In spite of these defects, Joblot's Microscopes show clearly a con- 

 siderable advance over those of his contemporaries, Leeuwenhoek, 

 Hartsoeker, Musschenbroek, Bonani, Wilson, and even John Marshall. 

 Most of Joblot's instruments are " simple Microscopes," and possess 

 proper focusing arrangement, with steady motion for the objective by 

 wheel and screw, and also efficient illumination with cylindrical dia- 

 phragms for excluding all extraneous light. One of them has a rotating , 

 stage. Joblot also invented some compound Microscopes, with three 

 and four lenses, but he does not appear to have been very satisfied 

 with these, because, though they gave him a larger field and greater 

 magnification, the images were less clear than those obtained with his 

 " simple " Microscopes, which is not to be wondered at. Several of the 

 apparatus he devised, such as forceps for holding objects, apparatus for 

 exhibiting the circulation of the blood, hollow-ground glass slides for 

 viewing living objects in liquids and pond-water,were very neat, efficient, 

 and well conceived. 



The objectives used by Joblot in his Microscopes were small bits of 

 glass, ground to a curved surface on both sides, thus making rough 

 bi-convex lenses of various foci (only one of the lens-holders now 

 contains the lens). In his text Joblot mentions object-glasses of 

 I to 12 lines focus ; the old Paris line was equal to 2*175 mm., there- 

 fore the range of his objectives appears to have been from about 

 h to 26 mm., or 7 V to l T ' e of an inch. He also describes a " Micro- 

 scope a liqueurs " (that is, for the examination of liquids), by means of 

 which " blown-glass lenses " (" lentilles soufflees et celles qui ne le sont 

 point ") can be employed, but he gives no description of these blown- 

 glass lenses, or how they were made. 



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