500 SUMMAKY OF CURRENT RESEARCHES RELATING TO 



are very long, preferably of some thin material. The writer has found 

 that ordinary green opaque window blinds can be sized black, so as to 

 become practically light-proof, and as it is advisable in constructing a 

 light trap to have two blinds, he finds that with two such blinds the 

 light is wholly excluded, and, if necessary, the room can be used as a 

 photographic dark-room. The wooden rollers used are of the ordinary 

 pattern, and present no special peculiarity. They are built in, or boxed 

 in, at the top in a light-tight manner. 



We turn next to the various sleeves sliding on the long, upright 

 girders. Of these one of the most important is the right-hand lower 

 sleeve, which carries a leg-of-mutton shaped table for use in connection 

 with the production of camera-lucida drawings. This sleeve, as well 

 as all the others, is balanced with a sash- weight, so that it moves with 

 the utmost freedom either up or down through a space of about 4 ft. 

 The table may, therefore, be placed within 15 in. of the floor, or it may 

 be raised to a distance of 3 ft. This adjustability is found to be highly 

 convenient in the production of camera-lucida drawings of definite 

 magnification. The peculiar shape of the table has been evolved from 

 practical experience during many years. In general, its form is such 

 that, when taken together with its mate on the other side of the Micro- 

 scope, it presents a semicircular curvature, which gives the investigator 

 a free play for hands and body. This table is painted black, as are all 

 the other accessories used in this system (see fig. 60, 33, 34). 



Turning to the left-hand side of the Microscope, we find an entirely 

 similar and symmetrical sleeve and table, which, however, is used for a 

 very different purpose. This sleeve carries the mate to the camera- 

 lucida table, and, of course, in the case of a left-handed operator, could 

 be used in the same way as the right-hand table would be used by a 

 right-handed operator. The usual position for the left-hand table is 

 about on a level with the Microscope stage. This height is found to be 

 convenient for several reasons ; first, under ordinary circumstances, it is 

 about ordinary table height, and is convenient for supporting dissecting 

 Microscope, which, as explained later on, has a special illumination of 

 its own. Thus, in the preparation and examination of objects, the 

 dissecting stand is as close as possible to the examination stand, and 

 the objects may be transferred from one to the other with the greatest 

 convenience ; a second reason for having the left-hand table on a level 

 with the stage of the Microscope, is that the preparations may be moved 

 on and off the stage of the Microscope with the least danger and with 

 the greatest facility. A third reason is that, in this position, the left 

 forearm finds it a most convenient rest in working the fine-adjustment 

 screw. In addition to the three sleeves already described, the long 

 girders carry two cross-pieces for the attachment of various accessories. 

 These wooden cross-pieces slide up and down, and are weighted with 

 sash -weights, so that their adjustment may be quickly and easily accom- 

 plished. In order that the friction on the girders may not cause any 

 inconvenience, arms extend upward from these cross-pieces for the 

 purpose of carrying pulleys which are in contact with the edges of the 

 girder, and so reduce the friction. These cross-pieces are clamped in 

 position by set-screws at the side. It will be at once evident that these 



