ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 837 



MICROSCOPY. 



o. Instruments, Accessories, &c* 



Nachet's Large Microscope. — The modern form of M. A. 

 Nachet's larger Microscopes is very familiar to English microsco- 

 pists, and in the latest modification of the " Grand Modele per- 

 fectionne " all the leading features are retained. The modifications 

 relate principally to (1) the fine-adjustment, (2) the substage, (3) the 

 mirror, and (4) the stage. 



The fine-adjustment is on the well-known Continental model, but 

 the action of the spiral spring is reversed, that is, it is now arranged 

 to draw the sheath connected with the body-tube downwards, in- 

 stead of pushing it upwards as formerly ; by this alteration the fine- 

 adjustment screw controls the movement by the contact of its point 

 with a hardened steel plate, greatly reducing the friction, whereas 

 formerly the screw passed through a nut against which the spiral 

 spring pressed upwards, causing much friction. The result is claimed 

 to be " a precision and smoothness quite remarkable," with, at the 

 same time, complete rigidity in consequence of the extent of tho 

 surfaces of contact in the prismatic column, so that the second 

 (Jackson) slow motion of the older form is not requiredi 



The substage is centering, and to change the condensers, &c, can 

 be turned back from the stage on a pivot, which can also be removed 

 when required, being attached to a short arm sliding in grooves in 

 the tail-piece and moved up and down by a lever. The pivot contains 

 a slow motion, allowing the illumination in the substage to be focused 

 very exactly on the object. 



The mirror is attached by a series of short arms with three 

 articulations acting at right angles to each other, so that it can be 

 moved in all directions for obtaining the effects of oblique light. Its 

 distance from the stage can also be varied. 



The modification of the stage is, however, the most striking of 

 the novelties, as it comprises an arrangement for observing the 

 approach of the objective to the cover-glass. It is thus described by 

 M. Nachet t :— 



" To the stage can be adapted at pleasure an arrangement which 

 is very useful in the examination of rare or precious slides. It is 

 composed of two small mirrors, one concave, placed at the level of the 

 stage on the left, and movable in all directions, so as to send rays of 

 light grazing the surface of the stage. The second one (plane) is 

 placed opposite on the right, and is inclined at 45°, so as to deflect 

 the rays vertically. The image of the end of the objective brightly 

 illuminated is received on the small mirror on the right, and at a 



* This subdivision contains (1) Stands; (2) Eye-pieces and Objectives; 

 (3) Illuminating Apparatus; (4) Other Accessories; (5) Photo-micrography; 

 (6) Manipulation ; (7) Microscopical Optics, Books, and Miscellaneous matters. 



t 'Catalogue descriptif des Instruments de Micrographio construits par A- 

 Nachet,' 61 pp., 72 figs., 2 heliographs, and 1 col. pi., 8vo, Paris, 1SS6. 



