THE COMPOUND MICROSCOPE 27 



feriority of the objective the image formed by it is 

 poor, a powerful ocular will but magnify and 

 accentuate its defects. In point, it is to the objec- 

 tive that we must turn for definition and detaU. 

 Thus an objective magnifying x 10 and an eye- 

 piece of similar power will give at a 10-inch tube- 

 length magnification of 100 diameters, but the 

 detail of the object -will be more defined if the power 

 of the objective be x 20 and the ocular x 5, although 

 the final magnification in both cases is x 100. 

 The worker's rule, then, should be to use an objec- 

 tive sufficiently good and powerful to bring out a 

 detailed and well-defined image of the object, and 

 an ocular which will present that image to the eye 

 in a satisfactory manner. Personally, I have Httle 

 use for high-power oculars. I use three with some 

 regularity ; my No. 2, magnifying x 6, is in most 

 common use ; next comes No. 3, x 8 ; and last 

 No. 1, X 5. These three eye-pieces in superior 

 mounts cost 10s. 6d. each ; they are to be got in the 

 student's pattern for 5s. each. 



Messrs. Watson make a series of " Parachromatic " 

 objectives which have many excellencies, and have 

 the recommendation of being relatively inexpensive. 

 The J-inch in this series costs £1 5s. ; the l-inch, £1 ; 

 and the 1^-, 2-, and 3-inch, £1 2s. each. Combined 

 with their No. 2 Huyghenian eye-piece, these objec- 

 tives, calculating a 7|-iach tube-length, give the 

 following total magnifications : 



3 in. Parachromatic Objective and No. 2 Ocular = x 16 

 2 „ „ „ „ =x 29 



H„ » >. " =x 36 



1 „ » >. " =x 50 



i. .. .. „ =x209 



