374 
ME. WAEEEN DE LA EIJE ON THE 
In both figures the same letter is employed to designate the same part, capital 
letters being used for the principal parts, and the same small letter, either alone or with 
one or more dashes, for the subordinate details attached to it. S is a tripod stand sup- 
Eig. 2. 
ported on the legs s ; to this stand is firmly fixed the arm E, which supports the fixed 
microscope M in the centre of the instrument. This microscope can be adjusted to 
focus by means of the milled head shown in the engraving; and its positive eyepiece 
can also be adjusted by sliding it up or down, so as to bring to focus wu’es crossing at 
right angles and fixed in the centre of the field of view in such a way that their dmections 
correspond respectively with the positions of the slides A and B, presently to be spoken 
of. E, fig. 1, is a plain mirror, which is adjustable so that it may reflect light through 
the photograph. A is a slide to which are attached all the other parts of the appa- 
ratus ; it moves freely, and without vibration, between guide-bars fixed on the top plate 
of the tripod stand, and shown in fig. 1. The top plate of the tripod stand has a round 
hole in it, and the bottom plate of the slide A is perforated with a similar hole. 
A steel rod a”, screwed for a certain distance at the point, works into a tapped hole 
in the slide A; by taking hold of the milled head a", the slide A may be rapidly moA’ed 
the whole length of the guide-bars, the rod carrying with it the clamping-piece with its 
two screws a”', a'”. These clamping-screws slide through two slotted holes in the top 
plate of the stand ; when the nuts a'", a'" are screwed tight the slide is held fast, but by 
turning the milled head a" the micrometer screw is also turned, and the slide can be 
moved for any short distance. 
Attached to the slide, and moving with it, is a scale a, a little more than 4 inches in 
