ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



087 



Fig. 143. 



as to make the advantage of the leverage 4 instead of 2 • 3 times ; the 

 finest wheel divisions then read 1/400,000 in. focal motion. 



The lever is very strong and rigid, and by a fork rests upon two 

 studs diametrically placed on the sliding tube carrying the objective. 



The sliding tube bears upon extremely thin edges so as to make 

 contact with as small surfaces as possible and thus minimize the 

 friction. It should be highly polished and trued with crocus and 

 paraffin, and when finished well supplied with chronometer oil. A 

 further advance would be to have the pivot holes of the lever jewelled, 

 drilled, and polished into a conoid form. Great care should be taken 

 to thoroughly " true " spherically the free end of the fine screw. 



Several degrees of strength were tried of the depressing springs, 

 acting as safety-guards on the objective touching " cover." That 

 finally selected (on reversing the instrument so that the objective 

 was vertical and the wrong way up) gave a resistance of 4 oz. Less 

 than this strength would be sufficient were 

 the Microscope used perpendicularly. " On 

 the extreme accuracy of simultaneous contacts 

 and pressures depends the steadiness of the 

 'image under high powers, which should never 

 dance in focusing ever so lightly, as it nearly 

 always does in most Microscopes." 



Mechanical Stages.* — Mr. A. Y. Moore " con- 

 demns such mechanical stages as have the milled 

 heads above the stage. They are all well enough 

 for amateur work — looking at mounted slides — 

 but the room is not there, and the usual form of 

 stage is to be preferred, even though the projection 

 of the milled heads may be such as to prevent the 

 complete rotation of the stage (and this is a very 

 nice point — to talk about)." 



Ultzmann's Saccharometer. — Dr. R. Ultz- 

 mann has designed a cheap saccharometer to be 

 used with any Microscope. The instrument (con- 

 structed by Eeichert, of Vienna) is a Mitscherlich 

 saccharometer of small size ; it requires no special 

 source of light, since when adapted to the Micro- 

 scope it is sufficiently illuminated by the concave 

 mirror. 



In fig. 143 a is the eye-piece and b the 

 objective of a small Galilean telescope, of which 

 the focus is at p ; c is the upper Nicol prism, to 

 the mounting of which is fixed a vernier ; d is the 

 glass tube which holds the sugar solution, p is the 

 plate of right- and left-handed quartz, and / is the 

 lower Nicol. In using the instrument the body- 

 tube is removed and replaced by the saccharometer ; the mirror is 

 then adjusted so as to send the light up the tube. 



* The Microscope, vi. (1886) pp. 80-3. 



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