ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



1057 



reflected light Allien required, as in tlie original arrangement. It is 

 3/4 in. long and 2 in. wide, and to it is attaclied by a strong bar a 

 stout brass disc or stage, witb a central aperture of 3/4 in. diameter, 

 the interval between it and the cylinder being 1/4 in, A thinner 

 brass disc of rather smaller circumference and similar central aper- 

 ture, but having its edge bordered by a projecting rim both above and 

 below, is kept in close apposition to the first by a coil of wire-spring 

 soldered to it and to the base of the internal circumference of the 

 brass cylinder. It is between these two discs that the slide is lightly 

 but firmly held, it being easy to move it without jerk or imevenness 

 in any direction. The shallower projecting rim, which is deficient in 

 front, should be about the depth of the thickness of an ordinary slide, 

 and is intended to prevent the possible pressure of cemented objects 

 between the discs when searching far from their centre. The de- 

 ficiency of the rim in front secures the cover-glasses from injury. 

 The other rim should be much deeper, its use being to keep the disc 

 central, and working within the cylinder when drawn down. Its 

 border is arched, and the points between the arches are bent out- 

 wards ; the centre one forming a convenient catch for the thumb of 

 the left hand when depressing the disc to introduce the object, and 

 the otbers steadying the movement in the 

 inside of the cylinder. There is also a small Fig. 232. 



pin attached to this rim, which works in a 

 tube fixed to the cylinder, securing perfect 

 steadiness. 



Microscope with Catgut Focusing 

 Adjustment. — In 1881 * Herr J. Ulmer 

 suggested the use of a silk thread for 

 obtaining a simple adjustment of the focus 

 of a Microscope, working very easily and 

 without "loss of time," The principle 

 was apparently adoi:)ted several years earlier 

 in the form shown in fig, 232, 



A piece of catgut is attached by its 

 two ends to the top and bottom of the fixed 

 sheath in which the body-tube moves, and 

 is wound once round a spindle with milled 

 head, which is screwed to the body-tube 

 and passes through a slot in the sheath. 

 On rotating the milled head the catgut 

 winds on the spindle, thus carrying the 

 body-tube up or down as desired. The 

 spindle travelling in the slot prevents any 

 rotation of the body-tube. For the purpose 

 of tiglitoiiing the catgut the upper end 

 is passed through a hollow screw working 



in a fixed socket. The axle of the spindle is milled to prevent tho 

 catgut slipping. 



* .Sec this Journal, ii. ^1882) ji. 400. 



