is required to be filled. With sensitive accumulators of this character hydraulic machinery is much used on board ships for steering them, and for loading, discharging and storing cargoes. _Water Pressure Engines_ or _Water Motors_ of a great variety as to useful details have been invented to take advantage of a natural head of water from falls wherever it exists, or from artificial accumulators or from street mains. They resemble steam engines, in that the water under pressure drives a piston in a cylinder somewhat in the manner of steam. The underlying principle of this class of machinery is the admission of water under pressure to a cylinder which moves the piston and is allowed to escape on the completion of the stroke. They are divided into two great classes, single and double acting engines, accordingly as the water is admitted to one side of the piston only, or to both sides alternately. Both kinds are provided with a regulator in the form of a turn-cock, weight, or spring valve to regulate and control the flow of water and to make it continuous. They are used for furnishing a limited amount of power for working small printing presses, dental engines, organs, sewing machines, and for many other purposes where a light motor is desired. The nineteenth century has seen a revolution in _baths_ and accompanying _closets_. However useful, luxurious, and magnificent may have been the patrician baths of ancient Rome, that system, which modern investigators have found to be so complete to a certain extent, was not nor ever has been in the possession of the poor. It is within the memory of many now living everywhere how wretched was the sanitary accommodations in every populous place a generation or two ago. Now, with the modern water distribution systems and cheap bathing apparatuses which can be brought to the homes of all, with plunger, valved siphon and valved and washout closets, air valve, liquid seal, pipe inlet, and valve seal traps, and with the flushing and other hydraulic cleaning systems for drains and cesspools, little excuse can be had for want of proper sanitary regulations in any intelligent community. The result of the adoption of these modern improvements in this direction on the health of the people has been to banish plagues, curtail epidemics, and prolong for years the average duration of human life. How multiplied are the uses to which water is put, and how completely it is being subjected to the use of man! Rivers and pipes have their metres, so that now the velocity and volume of rivers and streams are measured and controlled, and floods prevented. The supplies for cities and for families are estimated, measured and recorded as easily as are the supplies of illuminating gas, or the flow of food from elevators.