36 



THE APPARATUS IN GENERAL. 



The apparatus consists of a table 43 inches long and IS^/^ inches wide 

 on strong and adjustable iron supports. Upon this table rests the optical 

 bench on four adjustable iron legs which permit it to slide back and forth 

 on two iron traclis. This optical bench caiTies the arc lights and all other 

 accessories for illumination, except those which are a part of the micro- 

 scope; these are, naming them from the light forward, first the condenser, 

 which consists of two convexo-concave lenses four inches in diameter 

 mounted at the ends of a nickeled tube; the lens farthest away from the 

 light is adjustable in the carrying tube. Then comes the cooling cell, 

 the ray filters, the shutter, the biconcave lens and the field diaphragm (see 

 Fig. 1); all these parts are carried on two nickeled iron rods, and are 

 adjustable in height from right to left and from before backward on the 

 table. A second table placed at the end of this of the same width and 

 height resting also on adjustable iron supports, is 85 inches long and 

 carries the microscope, which has as substage parts the Abbe with its 

 iris diaphragm and an additional iris diaphragm immediately under the 

 object for use when the Abbe is swung out. It carries also an extensible 

 camera which can be drawn out so as to hold the ground glass and the 

 photographic plate at any distance from the object between 20 and 75 

 inches. 



As TO THE Support of the Microscope. 



It has hitherto been regarded as in principle wrong to have the micro- 

 scope on the same table with the camera; our experience convinces me 

 that this is a good arrangement, if it is accompanied by the other pre- 

 cautions we now have for keeping the microscope steady. As we received 

 our instrument the microscope bench was clasped by iron clamps to two 

 nickeled iron tubes which extend the entire length of the camera table 

 and carry also the camera. By this ari'angement any shaking of the 

 camera was communicated to the microscope directly and rendered the 

 preservation of the focus during the replacement of the ground glass 

 by the plate holder nearly impossible; not one in five of our exposures 

 with this an-angement was successful; something had to be done; we 

 could not put the microscope on a separate table without entirely changing 

 the means of controlling the fine adjustment, which is regulated by a rod, 

 with milled head fastened to the table under the camera and connected 



