278 SUMMARY OF CURRENT RESEARCHES RELATING TO 



fitting together accurately parallel. The image of the object to be measured 

 is brought between tliem and the ivory wheel, divided into hundredths, each 

 division representing with 1000 the one-millionth of an inch. Each revolu- 

 tion of this wheel is audibly marked by a spring catch ; besides this, an 

 adjusting screw serves to set the zero-jaw accurately, and teeth 50 to the 

 inch display the number of whole turns."] 



Engl. Mech., XLVIII. (1889) p. 389 (1 fig.). 



(4) Photomicrograpliy. 



Zeiss's large Photomicrographic Apparatus.— Dr. Zeiss supplies 

 for photomicrographic purposes the special stand shown in fig. 44, which 

 is generally similar in form and size to the other large stands of the 

 maker. There is, however, in addition, an unusually large stage, with 

 mechanical movements, rotating by rack and pinion, and having a wide 

 opening for use with a low-power objective giving a very large field of 

 view. The Abbe illuminating apparatus is so arranged that it can be 

 easily removed and replaced by special spectral, polarization, &c. appa- 

 ratus. The body-tube is also of an unusually large diameter, partly for 

 avoiding internal reflection, and partly to render possible the use of the 

 low-power objective. 



The Microscope is not attached to the same support as the camera, 

 but both parts are on separate stands, which it is claimed is more con- 

 venient for working. The stand, screwed to a metal support which is pro- 

 vided with three levelling screws, is set up at one end of the platform 

 A (figs. 45 and 46), which is adjustable for height. At the other end of 

 the platform is an angle-plate C, which supports an electric lamp ; while 

 the space between the lamp and the Microscope M is occupied by an 

 optical arrangement consisting of two stout metal rails carrying the 

 illuminating apparatus for use with sunlight, two vertical screens 

 E and F, movable by rack and pinion, which can be quickly turned on 

 one side, and again brought back exactly to their old position ; a plane 

 mirror G, adjustable in height, with coarse- and fine-adjustment in the 

 vertical as well as in the horizontal axis, in order to correct slight 

 irregularities in the course of the heliostat ; and a stand H for the 

 reception of glasses for yellow and blue absorption liquids. For the use 

 of the arc-lamp, as shown in fig. 46, there is a water-chamber T with 

 plate-glass ends for the absorption of the heat-rays, and a lens L for pro- 

 jecting the image of the carbon points on the ground-glass plate. On 

 the end of the metal support B is an arrangement a, by which the 

 movement of a Hooke's joint 6 with rod h' can be transferred to the 

 micrometer screw. This is effected by means of a toothed wheel which 

 can be brought into gear with the toothed wheel of the micrometer screw. 

 The tube carries a double socket h into which, by turning the camera, 

 slides a corresponding socket-piece attached to the end of the camera, 

 so that a very perfect light-proof connection between Microscope and 

 camera is effected without disturbing the former. The socket-piece can 

 be easily removed and replaced by a macroscopic objective for ordinary 

 photographic work. The camera K is mounted on a separate light but 

 solid cast-iron stand SS, provided with iron rails on which it can slide 

 smoothly by means of rollers. The total length of the camera when 

 fully extended is 1 • 5 m. 



In order to fit the apparatus for taking fluid preparations, the camera 

 is divided into two halves, of which the one nearest the Microscope can 

 be turned up vertically, as in figs. 47 and 48, or inclined at any angle. 



