7. Unit of Mass 317 8. Natural System of Standards 319 9. Subsidiary Units 320 10. Derived Units 321 11. Provisional Units 323 12. Theory of Dimensions 325 13. Natural Constants 328 14. Mathematical Constants 330 15. Physical Constants 331 16. Astronomical Constants 332 17. Terrestrial Numbers 333 18. Organic Numbers 333 19. Social Numbers 334 CHAPTER XV. ANALYSIS OF QUANTITATIVE PHENOMENA. 1. Analysis of Quantitative Phenomena 335 2. Illustrations of the Complication of Effects 336 3. Methods of Eliminating Error 339 4. Method of Avoidance of Error 340 5. Differential Method 344 6. Method of Correction 346 7. Method of Compensation 350 8. Method of Reversal 354 CHAPTER XVI. THE METHOD OF MEANS. 1. The Method of Means 357 2. Several Uses of the Mean Result 359 3. The Mean and the Average 360 4. On the Average or Fictitious Mean 363 5. The Precise Mean Result 365 6. Determination of the Zero Point 368 7. Determination of Maximum Points 371 CHAPTER XVII. THE LAW OF ERROR. 1. The Law of Error 374 2. Establishment of the Law of Error 375 3. Herschel’s Geometrical Proof 377 4. Laplace’s and Quetelet’s Proof of the Law 378 5. Logical Origin of the Law of Error 383 6. Verification of the Law of Error 383 7. The Probable Mean Result 385 8. The Probable Error of Results 386 9. Rejection of the Mean Result 389 10. Method of Least Squares 393 11. Works upon the Theory of Probability 394 12. Detection of Constant Errors 396 BOOK IV. INDUCTIVE INVESTIGATION. CHAPTER XVIII. OBSERVATION.