262 HOW TO SEE WITH THE MICROSCOPE. 



particular objective he may employ he may be in some 

 measure defeated in his efforts ; still we have to hope 

 that his endeavors will not result in time " totally 

 lost." 



Lesson First. Place the mount of Monmouth rhom- 

 boids on the stand, select the two-inch ocular, mak- 

 ing immersion contact with water or glycerine, as has 

 previously been directed. Place the collar of the ad- 

 justment in the middle of its run ; use the light from 

 the smallest kerosene hand lamp, placing the same about 

 seven inches to the left of the stage, the flarne to be on 

 a level with the same, edgewise to the mirror, and two 

 inches in advance of the front edge thereof. Kemoving 

 all sub-stage appliances, swing the radial bar so that the 

 mirror shall give illumination, say from 70 axis; ma- 

 nipulate so as to light up the field, using about one-half 

 the sized flame your lamp will allow. Now focus, and 

 having taken a general look at the " tout ensemble," 

 select a frustule somewhat below a medium one in size, 

 and bring to the centre of the field, the valve in a hor- 

 izontal position. Now focus a^ain carefully, adjusting 

 the mirror so as to get the very best view attainable. 

 Now study for a moment the general character of the 

 image. Notice particularly if there be any distortion, 

 or whether the two ends are more or less indistinct or 

 obscured. Slide the object carrier and hunt up several 

 other shells and examine individually, that ;you may be 

 assured that you have a fair specimen to deal with. 

 Next, notice the edges of the valve ; compare the upper 

 with the under; note if these are tolerably clean and 



