ZOOLOGY AND BOTANY, MICROSCOPY, ETC. G49 



The substage-fitting is arranged to swing onfc of the optical axis with 

 the condenser or other apparatus which may be carried in it, and a fine- 

 adjustment is provided to the substage when required. 



Quidor-Nachet Microscope.* — The purpose of this instrument is 

 photomicrographic, with especial reference to stereoscopy. The Microscope 

 is described, and has been designed, by A. Quidor. The manufacture is 

 by Nachet. As will be seen from fig. 88 and pi. XIL, this instrument 

 differs from the ordinary model by the inclination which the Microscope 

 tube can take to the left and to the right of the vertical, and by the 

 independence of the stage P. An iris-diaphragm placed above the 

 revolver is used with weak objectives, thereby increasing the depth. 

 Inclination is measured by a graduated drum E. A clamp-screw S fixes 

 the apparatus in any desired position. The milled heads F control the 

 rackwork focusing in the usual way. The stage not only has rotatory 

 and rectangular movements, but can also be moved "vertically by means 

 of the micrometer-screw L. An index I coincides with a definite point 

 on the stage support when the upper surface of the latter coincides with 

 the axis of rotation. The independence of the stage makes it possible 

 to bring the upper face of the object to the level of this axis, a condition 

 indispensable if the object is to be, and to remain, centred during the 

 angular displacement of the optic axis of the Microscope. The camera 

 is placed above the Microscope-tube, and takes, automatically and succes- 

 sively, on the same plate (8 x 16 cm.) and at two different angles, two 

 views of the same object. The photography is performed with or with- 

 out the ocular. In fig. 88, AB and A'B' are two successive positions of 

 the frame for taking a stereoscopic cliche. D is the rod carrying the 

 camera. T is a double tube for preventing all infiltration of diffused 

 light ; b is one of the buttons controlling the rectangular movement ; 

 c is the axis of rotation. Fig. 88 also shows the arrangement for magni- 

 fications less than 8 diameters and for reductions. 



The author gives a table of the magnifications obtainable. They 

 may extend to 680 diameters. 



The author also explains and enunciates the two following principles 

 which govern the use of his Microscope : — 1. For the same inclination 

 of the optic axis the relief given by stereoscopic views of the same object 

 is independent of the magnification. 2. When an object is photographed 

 under an angle of inclination I x , its relative relief for a new inclination I 2 

 is multiplied by the square root of the ratio of the new angle of inclina- 

 tion to the first. 



The author adds many practical hints. An aquatic animal should 

 be photographed in water. Small animals between 4 and 40 mm. should 

 be fastened by a drop of gelatin to the bottom of a small dish and then 

 covered with water. The gelatin may be allowed to dry hard, or may 

 be set with a drop of formol. Smaller animals should be fixed with 

 osmic acid and mounted on a slide with formolated water. Animals 

 exceeding 40 mm. should in general be photographed dry. As an illumi- 

 nant sunlight, when obtainable with a heliostat, is excellent. Nachet's 

 form of the Nernst lamp is the most trustworthy ; it can be worked with 



♦^Arch. Zool. I3xper. et G6n., v. (1910) p. lxvii-lxxxi (5 figs.). 

 Oct. 19th, 1910 2 X 



