. The Ontario high school physics. the pipe G connecting them if the water is at a higher level in A than in B; or, whatamounts to the same thing, ifthe hydrostatic pressure at a isgreater than that at h. Thetank B may already have morew^ater in it, but the flow doesnot depend on that. It is regu-lated by the diflference betweenthe pressures at the two ends of the pipe and it Avill continueuntil these pressures become equal. Or, consider what happens when two gas-bags filled withcompressed air are joined by a tube in which is a the pressure of the air is the same in each there wil
. The Ontario high school physics. the pipe G connecting them if the water is at a higher level in A than in B; or, whatamounts to the same thing, ifthe hydrostatic pressure at a isgreater than that at h. Thetank B may already have morew^ater in it, but the flow doesnot depend on that. It is regu-lated by the diflference betweenthe pressures at the two ends of the pipe and it Avill continueuntil these pressures become equal. Or, consider what happens when two gas-bags filled withcompressed air are joined by a tube in which is a the pressure of the air is the same in each there will be noflow from one to the other on opening the stop-cock. If thereis a difference, there will be a flow from the bag at highpressure to that at low. Again, when two bodies at different temperatures arebrought together, there is a flow of heat from the one at thehigher temperature to that at the lower temperature. Corresponding to pressure in hydrostatics and to tempera-ture in the science of heat, in electricity we use the term. Fig. 473.—Water flows from the higher levelin A to the lower level in B. NATURE OF ELECTRICITY 389 potential, (or sometimes livessure). If two points of a con-ductor are at different potentials there will be a flow fromthe point at high potential to that at low potential. Thispotential difference (for which is an abbreviation), isusually measured in volts, a definition of which will be givenin the next chapter (§ 471). 454. Nature of Electricity. So far no reference has beenmade to the nature of electricity; indeed it is very difficult tomake a hypothesis which will explain satisfactorily all theobserved phenomena. We speak of a flow of electricity, but certainly nothing ofthe nature of ordinary matter moves, though just as certainlythere is a transference of energy. In the case of conductionof heat we do not know the precise nature of heat, but hereagain we are sure that there is a transference of energy. But we have electricity of two kinds,
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