212 



PRACTICAL MICROSCOPY. 



glass slide. To any one accustomed to focus by the old 

 method the present system will be found a consider- 

 able improvement, it being easy under these conditions to 

 obtain a sharp focus with an ordinary paraffin lamp when 

 using the T V objective. (See Fig. 193.) 



The microscope stand employed by the author possesses 

 a fine adjustment, moving the objective -^-^ of an inch 

 for each revolution of the milled head, and is divided into 

 twenty parts. His objectives require the following cor- 

 rections : 



The source of illumination may be the ordinary micro- 

 scopical paraffin lamp, as the light from it is much more 

 actinic than that of gas, and for all powers below the 

 J-inch it is only necessary to use the bull's-eye condensers 

 as shown in the figures. 



A very intense illumination, for photo-micrography, may 

 be obtained from paraffin oil by using it in a triple-wick 

 lamp, such as the Triplexicon or Sciopticon, with a con- 

 denser parallelising the rays proceeding from it, as shown 

 in Fig. 195. These parallel rays are again to be converged 

 by a convex lens of 3 inches diameter and 10 inches focus. 

 Such an arrangement as used by the author is shown by 

 Fig. 195, and by means of it the relative lengths of 

 exposure have been very much shortened. 



With the objectives already alluded to, the sensitive 

 plate being at a distance of 24 inches from the object, with 



