CONTENTS. 



BOOK IV. 



INDUCTIVE INVESTIGATION. 

 CHAPTER XVIII. 



OBSERVATION. 

 SECTION PAGE 



1. Observation 399 



2. Distinction of Observation and Experiment 400 



3. Mental Conditions of Correct Observation . 402 



4. Instrumental and Sensual Conditions of Correct Observation . 404 



5. External Conditions of Correct Observation 407 



6. Apparent Sequence of Events 409 



7. Negative Arguments from Non-Observation 411 



CHAPTER XIX. 



EXPERIMENT. 



1. Experiment 416 



2. Exclusion of Indifferent Circumstances 419 



3. Simplification of Experiments 422 



4. Failure in the Simplification of Experiments 424 



5. Removal of Usual Conditions 426 



6. Interference of Unsuspected Conditions 428 



7. Blind or Test Experiments 433 



8. Negative Results of Experiment 434 



9. Limits of Experiment 437 



CHAPTER XX. 



METHOD OF VARIATIONS. 



1. Method of Variations 439 



2. The Variable and the Variant ....... '. UO 



3. Measurement of the Variable ...!!' 441 



4. Maintenance of Similar Conditions ... ' 443 



5. Collective Experiments . . . 



6. Periodic Variations '.'.'.'. ."447 



7. Combined Periodic Changes ' " 450 



8. Principle of Forced Vibrations . . 



9. Integrated Variations .' i !!!!.' 452 



