132 THE AMERICAN MONTHLY [Aug 



the hole in the front of the camera. The base board 

 should be 8 inches wide, 8 feet long, and 1 inch thick — 

 2 inches in thickness is better. It should be well planed 

 on one surface. Beech, mahogany, or oak are the best 

 woods, pine should not be used. Draw a straight line 

 down the middle of the planed surface, the use of which 

 will be seen afterwards. 



The microscope may be of any pattern provided the 

 body may be turned absolutely horizontal. Most modern 

 microscopes can be placed in this position^ but frequently 

 they are unsteady when so placed. In such a case have 

 two iron shoes screwed to the long base-board, and under 

 these shoes slip two of the legs of the microscope ; for 

 the third foot have a hinged shoe with screw so that it 

 can be placed over the foot and screwed up tight so as to 

 hold it steadily. Some modern microscopes have a 

 horseshoe foot, in which case procure about four pounds 

 of lead in a block and place this over the foot. 



The microscope should have a substage condenser, but 

 if this does not form part of the outfit, then a low power 

 objective should be placed below the stage. 



The objective will, of course, be already part of the 

 outfit, but for those who wish to purchase new ones, 

 there are few which can beat the new hard semi-apochro- 

 mats of Mr. Reichert, of Vienna, a 3 mm. of this type of 

 quite new construction having passed most successfully 

 through some very severe tests. Still, good work can 

 be done with an inch, half-inch, or quarter-inch, though 

 better work can of course be done with fine diatom mark- 

 ings, etc. , with a one-sixth or one-eighth. 



In ordering new objectives it is essential to insure 

 their being corrected for the chemical rays, though with 

 anything higher than a one-sixth inch this can be ignored. 

 For objectives of lower power it is advisable to use a 

 strong tincture of litmus in a flat-sided cell or tank of 



