ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 497 



building is a large block of cement weighing several tons. In this block 

 of cement three T-girders, two of which are approximately 8 in. in each 

 dimension, are imbedded vertically to the depth of about 4 ft. The 

 central one of the girders carries the Microscope, together with certain 

 accessory apparatus connected with the illumination of the object. This 

 girder is much smaller and shorter than the other two, extending only 

 about 18 in. above the floor of the Microscope room. The other two 

 girders are mates and extend to within about 18 in. of the ceiling of the 

 room ; in other words, project upward into the room about 11 ft. 



Needless to say, the object of these girders is to afford attachment 

 for all the necessary apparatus connected with the Microscope. The 

 girders at every part clear the walls of the building by a fair margin. 

 It is, however, best to place all the girders as close to the Microscope 

 window as is convenient. The reason for this will be explained on a 

 subsequent page. In the present instance the distance between the 

 girders and the window casings is about 1 in. The general principle on 

 which the accessory apparatus is attached to the girders is that of sliding 

 metal sleeves that may be clamped in any desired position. A sleeve of 

 ^ in. sheet metal surrounds the small central girder and projects 

 outwards — that is, towards the observer — sufficiently to form a base on 

 which the Microscope may rest. This base is from 1-2 times larger 

 than the horse-shoe base of the Microscope. This gives a sufficient 

 amount of space, so that the Microscope can be readily arranged for 

 different classes of work, moved sidewise in either direction, or forwards 

 or backwards. The sleeve carrying the Microscope is clamped to its 

 pillar by 3 set-screws, and by means of this simple arrangement the 

 Microscope can be raised and lowered to suit different operators and 

 different classes of work. When, for instance, micro-photographs are 

 being taken, it is most convenient to drop the sleeve to its lowest limit, 

 so that the Microscope will rest on a base about 15 in. above the floor. 

 For most photo-micrographic work this will enable the operator to bring 

 the focusing plate of the camera (Fig. 60, 19) low enough to render it 

 unnecessary for the operator to have any special step-ladder to assist him 

 in obtaining an accurate focus. On the other hand, when it is necessary 

 to place the Microscope high and the camera-lucida table low, one can 

 obtain a distance as great as 2^ ft. between the level of the eye-piece of 

 the Microscope and the drawing table. This, together with the peculiar 

 camera-lucida, which will be described later on, enables one to make his 

 original sketches of such a size as to allow for that liberal reduction in 

 the subsequent photographic process which gives the best results for 

 book illustrations. The sleeve which carries the Microscope also carries 

 a wooden front as wide as the Microscope window and about 2 ft. deep 

 — in other words, about 3 ft. by 2 ft. This screen, which of course 

 slides up and down with the Microscope and its sleeve, carries two aper- 

 tures. One of these apertures is in front of the Microscope mirror, and 

 is designed to allow the light from the special out-door illuminating 

 screen to strike the mirror and pass through the Microscope. The 

 second aperture is of much larger size, and is glazed with ground glass 

 and opened or closed as desired by means of a hanging slide worked 

 by foot-power. The object of this second opening is to secure a correct 



