500 



APPENDIX. 



MR. KINGSLEY S ILLUMINATOR. 



Fig. 270. 



This instrument, the 

 invention of the Rev. 

 W. Kingsley, of Cam- 

 bridge, is represented 

 in fig. 270, as con- 

 structed by Mr. Ross ; 

 it consists of three 

 lenses, of very large 

 diameter, for their focal 

 length, for the purpose 

 of producing a large 

 angular pencil of light, 

 the forms of the lenses 

 being given in section 

 at the upper part of the 

 figure. The illumina- 

 tor is applied either to 

 the under surface of the 

 stage, in the usual man- 

 ner, or is made to fit 

 into the tube, a a, re- 

 presented in plate xi. ; 



to its under surface is fixed a revolving diaphragm plate, the 

 image of which is to be formed in the same plane as that in 

 which the object is situated, as in the WoUaston condenser. 

 Mr. Ross's plan of using this instrument, and bringing out the 

 effect produced by Mr. Kingsley, is as foUows: — First, as 

 usual, let the image of an aperture in the diaphragm plate be 

 produced in the centre of the field of the microscope, at the 

 same time that the object is distinctly seen, then, by means of 

 the adjustable stage, place the object on one side of the field of 

 the microscope, and follow it by moving the compound body ; 

 pursue this course untU the object is laterally just beyond the 

 margin of the image of the aperture; whilst the object is in this 

 position, and the image of the aperture is just without the 



