ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 421 



screws, thus rendering the upper portion of the instrument ready for 

 use in examining large surfaces — the stage, with its plate removed, 

 serving as a base. The arm embodies two special features : (1) It 

 provides for extraordinary range of working distance up to 155 mm., 

 measuring from lower edge of nose-piece to stage ; the curved part is 

 adjustable along upright, and can loe fixed in any position by the 

 clamping head shown in opening of curved part ; the working distance 

 can also be decreased by detaching curved part from upright and body- 

 tubes, inverting and replacing it, for focusing some distance beneath 

 stage. (2) The entire arm with body-tube can be removed and used 

 on a stand consisting of base-plate and vertical pillar (listed as K B), it 

 being only necessary to place a short post, as provided, in socket at back 

 of arm. The body-tubes are a combination of two Microscope tubes, 

 the upper parts of which are fitted with porro prisms, and are rotataljle 

 for adjusting position of eyepieces to ol)server's pupillary distance ; one 

 image merges with the other, and the object is seen stereoscopic-ally, 

 erect and not transposed ; the nose-piece provided takes self-centring 

 slides, upon which each pair of objectives is mounted, with means for 

 centring one with the other ; one of each pair of objective mounts 

 provides for adjustment to compensate for differences between the 

 observer's eyes. The focusing adjustment is by standard rack-and- 

 pinion, the pinion heads being so placed with relation to body-tubes as 

 to eliminate completely the inconvenience caused when these parts are 

 close together ; the location of rack slide is such that it is not immersed 

 when Avorking with water-immersion objectives. The stage is of metal 

 with large rectangular aperture provided with two removable plates, one 

 of glass 80 X 95 mm., the other of metal, same size, with aperture 

 22 mm. in diameter, underneath which a rotating plate provides white 

 opaque, black opaque, and ground-glass stops, or clear aperture ; the 

 stage is also provided with detachable metal hand rests and spring clips. 

 The mirrors are plane and convex, 50 mm. in diameter, adjustable in 

 two planes in a fork ; they are mounted on a swinging arm, and are 

 not easily removable. 



(3) Illuininating- and other Apparatus. 



New Mechanical Stage.* — Katharine Heanley, who describes this 

 new device, says that in addition to the usual advantages of a mechanical 

 stage, the invention here illustrated (fig. 29) is easily fixed to and 



SPRING 

 FINGER 



Fig. 29. 



unfixed from any Microscope. This is effected very simply. To the 

 right, on the under side of the machine, is a strong curved leaf spring 

 attached at its proximal end to a firm crossbar ; on the left, at a 



* Lancet, July 15, 1916, p. 110 (1 fig.). 



