In compressed air machines the losses of pressure due to incomplete expansion, cooling, and waste spaces, play an important part. In water pressure machines loss does not occur from these causes, on account of the incompressibility of the liquid, but the frictions of the parts are the principal causes of loss of power. It would be advisable to ascertain whether, as regards this point, high or low pressures are the most advantageous. Theoretical considerations would lead the author to imagine that for a piston machine low pressures are preferable. In conclusion, the following table gives the efficiencies of a Girard turbine, constructed by Messrs. Escher Wyss & Co., of Zurich, and of a Schmid machine, as measured by Professor Fliegnor, in 1871: ESCHER WYSS & CO'S TURBINE. Effective Head of Water. Revolutions Efficiency. per minute. Meters. Feet. Revs. Per cent. 20.7 67.9 628 68.5 20.7 67.9 847 47.4 24.1 79.0 645 68.5 27.6 90.5 612 65.7 27.6 90.5 756 68.0 31.0 101.7 935 56.9 31.0 101.7 1,130 35.1 SCHMID MOTOR. 8.3 27.2 226 37.4 11.4 37.4 182 67.4 14.5 47.6 254 53.4 17.9 58.7 157 86.2 20.7 67.9 166 89.6 20.7 67.9 225 74.6 24.1 79.0 238 76.7 24.1 79.0 389 64.0 27.6 90.5 207 83.9 It will be observed that these experiments relate to low pressures; it would be desirable to extend them to higher pressures. IV. _Transmission by Electricity._--However high the efficiency of an electric motor may be, in relation to the chemical work of the electric battery which feeds it, force generated by an electric battery is too expensive, on account of the nature of the materials consumed, for a machine of this kind ever to be employed for industrial purposes. If, however, the electric current, instead of being developed by chemical work in a battery, is produced by ordinary mechanical power in a magneto-electric or dynamo-electric machine, the case is different; and the double transformation, first of the mechanical force into an electric current, and then of that current into mechanical force, furnishes a means for effecting the conveyance of the power to a distance.