BOOK IV.

THE PHILOSOPHY OF THE SECONDARY MECHANICAL SCIENCES.

CHAP. I. OF THE IDEA OF A MEDIUM AS COMMONLY EMPLOYED 293

_Art._ 1. Of Primary and Secondary Qualities. 2. The Idea of Externality. 3. Sensation by a Medium. 4. Process of Perception of Secondary Qualities.

CHAP. II. ON PECULIARITIES IN THE PERCEPTIONS OF THE DIFFERENT SENSES 302

_Art._ 1. Difference of Senses.

_Sect._ I. _Prerogatives of Sight._ _Art._ 2. Position. 3. Distance. {xv} _Sect._ II. _Prerogatives of Hearing._ _Art._ 4. Musical Intervals. 5. Chords. 6. Rhythm.

_Sect._ III. _The Paradoxes of Vision._ _Art._ 7. First Paradox. 8. Second Paradox. 9. The same for near Objects. 10. Objections answered.

_Sect._ IV. _The Perception of Visible Figures._ _Art._ 11. Brown's Opinion.

CHAP. III. SUCCESSIVE ATTEMPTS AT THE SCIENTIFIC APPLICATION OF THE IDEA OF A MEDIUM 322

_Art._ 1. Introduction. 2. Sound. 3. Light. 4. Heat.

CHAP. IV. OF THE MEASURE OF SECONDARY QUALITIES 333

_Sect._ I. _Scales of Qualities in General._ _Art._ 1. Intensity. 2. Quantity and Quality.

_Sect._ II. _The Musical Scale._ _Art._ 3. Musical Relations. 4. Musical Standard.

_Sect._ III. _Scales of Colour._ _Art._ 5. The Prismatic Scale. 6. Newton's Scale. 7. Scales of Impure Colours. 8. Chromatometer.

_Sect._ IV. _Scales of Light._ _Art._ 9. Photometer. 10. Cyanometer.

_Sect._ V. _Scales of Heat._ _Art._ 11. Thermometers. 12. Their progress. 13. Fixed Points. 14. Concordance of Thermometers. 15. Natural Measure. 16. Law of Cooling. {xvi} 17. Theory of Exchanges. 18. Air Thermometer. 19. Theory of Heat. 20. Other Instruments.

_Sect._ VI. _Scales of other Quantities._ _Art._ 21. Tastes and Smells. 22. Quality of Sounds. 23. Articulate Sounds. 24. Transition.