ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



77 



pass through the centre of the hemisphere H. When the ocular is 

 tilted about the hinge A, the limit-line can be brought into its axis, and 

 therefore can be read off with all desirable sharpness. 



Watson-Conrady Condenser Vertical Illuminator.* — This instru- 

 ment is shown in fig. 10, and is intended to obviate the difficulties 

 experienced in working with a vertical illuminator. The objects attained 

 by this piece of apparatus are : — 1. Bringing the illumination under a 

 control as complete as that which is obtained with transparent objects 

 and the best substage apparatus. 2. Obtaining the brightest possible 

 illumination from small sources of light. 8. Simplifying and rendering 

 certain the correct placing of the illuminant, whether it be supplied as a 

 fixed portion of the apparatus or separately. 4. Rendering unnecessary 

 the usual short mounting to objectives for metallurgy. Reference to 

 the diagram will show that it is built on the plan of a condenser system 

 in miniature complete with lenses and iris diaphragm. The reflector, 

 which is mounted in a central box, is a large transparent plate. For 

 general purposes a small 4-volt electric lamp may be fixed in a suitable 

 position at the end of the condenser system, and, when work is to be 



Pig. 10. 



done, it is only necessary to switch on the current from the battery and 

 everything will be found to be in good order. With this an illumina- 

 tion can be obtained sufficient for visual or photographic purposes. A 

 specially constructed 25 caudle-power lamp of small size is also supplied 

 with fittings to attach to the illuminator, and this lamp can be connected 

 to the ordinary current supply. If an independent illuminant is used, 

 it should be set about 1^ in. from the outer end of the tube. Any 

 small source of light can be used, such as the edge of an oil lamp flame, 

 or, if a very brilliant illumination is required for projection, a small 

 arc-lamp should be used, such as the makers' " Argus." 



The apparatus is used in the following manner : — The illuminator is 

 attached to the nose-piece of the Microscope, the objective is screwed 

 into it, and approximately focused on the polished metal objects. The 

 light is turned on, and the illumination is then regulated by the inner 

 iris diaphragm so as to cover the extent of the object actually under 

 observation. This eliminates a large amount of stray light, and a con- 

 sequent gain in contrast in the image is obtained. The iris dia- 

 phragm nearest the illuminant is then used in precisely the same manner 

 as that of the ordinary substage condenser, and by its means the cone 



* W. Watson and Sons' Special Catalogue : Microscopes and Accessories for 

 Metallurgy, pp. 28-9. 



