CONTENTS. 



BOOK IV. 



INDUCTIVE INVESTIGATION. 

 CHAPTER XVIIL 



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. Removal 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 



