THE WOODWARD ILLUMINATOR. 175 



mirror away from the lamp, placing it so that the gradu- 

 ating wheel shall read at about 34, 35 or 36 degrees. 



The lamp being passed to the right or left of the stage, 

 as the case may be, and about four inches distant there- 

 from, bring the edge of the flame to the mirror; now 

 move the lamp to or from the front edge of the table, 

 so that the edge of the lamp frame, prism and centre of 

 mirror shall form approximately a straight line parallel 

 with the front edge of the table, 



From the position described it will be seen that the 

 ordinary sub-stage would be entirely in the way; hence 

 the necessity for its removal. 



Making immersion contact, focus your objective, and, 

 without changing the position of the swing bar, manip- 

 ulate the mirror so that the field may be nicely illumi- 

 ated, select your object, which we take it for granted 

 will be 3ome difficult lined test. 



Next, interpose the large bull's-eye condenser (flat 

 side to the lamp), thus concentrating light on the mir- 

 ror ; adjust the object glass. 



It will be well now to try the effect of various degrees 

 of obliquity, remembering that any considerable move- 

 ment of the swing- bar will necessitate a new adjustment 

 of the condenser. A slight change, too, in the position 

 of the lamp will sometimes be attended with excellent 

 results, keeping, in all cases, however, its edge to the 

 mirror. 



The above includes the author's method of working 

 the Woodward prism ; but as this accessory bids fair to 

 come into general use he will now traverse the ground 



