CONTENTS, 



BOOK IV. 



INDUCTIVE INVESTIGATION. 

 CHAPTER XVIII. 



OBSERVATION. 

 SECTION PAGE 



1. Observation 1 



2. Distinction of Observation and Experiment .... 2 



3. Mental Conditions of Correct Observation .... 4 



4. Instrumental and Sensual Conditions of Correct Observation . 7 



5. External Conditions of Correct Observation . . . .10 



6. Apparent Sequence of Events . . . . . .13 



7. Negative Arguments founded on the Non-Observation of 



Phenomena . . . . . . . . .16 



CHAPTER XIX. 



EXPERIMENT. 



1. Experiment 22 



2. Exclusion of Indifferent Circumstances . . . .26 



3. Simplification of Experiments . . . . . .30 



4. Failure in the Simplification of Experiments . . .33 



5. Eemoval of Usual Conditions . . . . . .35 



6. Interference of Unsuspected Conditions . . . .37 



7. Blind or Test Experiments 43 



8. Negative Results of Experiment . . . . . .45 



9. Limits of Experiment ....... 48 



CHAPTER XX. 



METHOD OF VARIATIONS. 



1. Method of Variations 50 



2. The Variable and the Variant 51 



3. Measurement of the Variable . . . . . .53 



4. Maintenance of Similar Conditions ..... 55 



5. Collective Experiments 57 



6. Periodic Variations . . . . . . . .61 



7. Combined Periodic Changes . . . . . .63 



8. Principle of Forced Vibrations ...... 65 



9. Integrated Variations . . . . . . .67 



