POSITION OF OBSERVER. 247 



tion at the work table as will allow him to observe for 

 hours without serious fatigue. Such a table as has 

 already been recommended, with two front drawers, 

 will be just what is wanted. The novice is here re- 

 minded that in working- with the higher powers, after 

 having placed the object in position under the objective, 

 the latter being correctly adjusted, there will be no 

 longer use for the coarse adjustment. Having, then, 

 our table, place the chair adjacent thereto, but in place 

 of putting its front edge parallel to the front of the 

 table, as is generally done, turn the chair to the right 

 until the front and left-hand sides form equal angles 

 with the front of the table, the angular point formed 

 by the meeting of the front and left-hand edges of the 

 chair being adjacent to the table. Now let the observer 

 seat himself, placing the shank of the left shoe on the 

 left-hand round of the chair. Pull out both drawers, 

 so that the edge of these, assisted by the edge of the 

 table, shall form a double rest for the forearm. Now 

 place the stand in such a position, that is, with refer- 

 ence to the front of the table, that the left hand finds 

 its way easily to the fine adjustment, while that of the 

 right grasps the mirror bodily, the tube being mean- 

 while adjusted to the standard length, and the whole 

 instrument properly inclined. Let the reader practice 

 these directions thoroughly until he shall be able to 

 thus sit at his instrument firmly wedged to it. It will be 

 noticed that, once in this position, either hand can grasp 

 the object slide for the purpose of making any neces- 

 sary change, and without seriously disturbing the double 



