INDEX. GENERAL METHODS OF PHYSICAL INVESTIGATION. ANALYTICAL METHOD. Mean, 3. Probable Error, 3. Weights, 4. Probable Error of Interpolation, 12. Residual Curves, 12. Maxima and Minima, 13. Three Variables, 14. PHYSICAL MEASUREMENTS Time, 16. Weight, 19. Length, 19. Areas, 22. Volumes, 22. 11 16 GENERAL METHODS OF PHYSICAL INVESTIGATION. THE object of all Physical Investigation is to determine the effects of certain natural forces, such as gravity, cohesion, heat, light and electricity. For this purpose we subject various bodies to the action of these forces, and note under what circumstances the desired effect is produced; this is called an experiment. Investigations may be of several kinds. First, we may simply wish to know whether a certain effect can be produced, and if so, what are the necessary conditions. To take a familiar example, we find that water when heated boils, and that this result is attained whether the heat is caused by burning coal, wood or gas, or by concentrating the sun's rays; also whether the water is contained in a vessel of metal or glass, and finally that the same effect may be produced with almost all other liquids. Such work is called Qualitative, since no measurements are needed, but only to determine the quality or kind of conditions necessary for its fulfilment. Secondly, we may wish to know the magnitude of the force required, or the temperature necessary to produce ebullition. This we should find to be about 100° C. or 212° F., but varying slightly with the nature of the vessel and the pressure of the air. Thirdly, we often find two quantities so related that any change in one produces a corresponding change in the other, and we may wish to find the law by which we can compute the second, having given any value of the first. Thus by changing the pressure to which the water is subjected, we may alter the temperature of boiling, and to determine the law by which these two quantities are connected, hundreds of experiments have been made by physi |