TO THE STUDENT 3 



whether your specimen is abnormal, or whether 

 your observation of it is at fault in any way. 

 Always try to see all you can with the unaided eye 

 before resorting to the aid of a hand lens or microscope. 

 C. Experimentation: 



6. In mere observation one takes conditions as he finds 

 them; in experimentation, he determines, within 

 limits, the conditions under which the observation 

 is made. It is never possible to control, absolutely, 

 all the conditions in any experiment, but this is 

 partly compensated for by arranging side by side of 

 the experiment proper, a check or control. In the 

 experiment and control all conditions should be as 

 nearly alike as possible save one. The golden rule 

 in experimenting is: vary only one condition at a 

 time. Then if the experiment and. control give 

 unlike results, we are justified in attributing the 

 difference to the unlike factor. 



7. Before beginning an experiment, the object, or aim, 

 of the experiment must be clearly conceived and 

 clearly stated. The necessary materials and ap- 

 paratus should next be decided upon and procured. 

 Then may follow the operation, that is, the arrange- 

 ment of the materials and apparatus in a suitable 

 way. This step is frequently referred to as "set- 

 ting up" the experiment. The record of it should 

 include an accurate statement of the conditions at 

 the beginning of the experiment, together with 

 drawings of the apparatus and material as the 

 experiment is set up. 



Next follows the observation, which must always be 

 made and recorded at the time and place of the experi- 

 ment. It should include suitable drawings. Fin- 

 ally, there may be stated the inference, that is, the 



