He finds, for example, from the diagram that the initial leakage of 2000 gallons an hour has in the course of a 41 hours' night inspection fallen to 400 gallons an hour, and that the 1600 gallons an hour is accounted for by Distribution The earliest water supplies in Great Britain were generally distributed at low pressure by wooden pipes or stone or brick conduits.
The rate of circulation in the ordinary low pressure hot-water system may be considerably accelerated by means of steam injections.
The characteristic feature of the south-western Pacific is therefore the relatively low pressure and the existence of a true monsoon region in the middle of the tradewind belt.
If placed upon Europe it would extend from Rome to the North Cape, but latitude is of course only one of the factors influencing climate, the arrangement of the ocean currents and of the areas of high and low pressure making a very wide difference between the climates of the two sides of the Atlantic. In reality the Pacific coast of Canada, rather than the Atlantic coast, should be compared with western Europe, the south-west corner of British Columbia, in lat.
Although of reduced strength in the summer, they still suffice to dominate weather changes; it is during the approach of a low pressure centre that hot southerly winds prevail; they sometimes reach so high a temperature as to wither and blight the grain crops; and it is almost exclusively in connection with the cloudy areas near and south-east of these cyclonic centres that violent thunderstorms, with their occasional destructive whirling tornadoes, are formed.
The warmed air of summer produces an area of low pressure in the west-central United States, which interrupts the belt of high pressure that planetary conditions alone would form around the earth about latitude 30; hence there is a tendency of the summer winds to blow inward from the northern Pacific over the Cordilleras toward the continental centre, and from the trades of the torrid Atlantic up the Mississippi Valley; conversely in winter time, the cold air over the lands produces a large area of high pressure from which the winds tend to flow outward; thus repelling the westerly winds of the northern Pacific and greatly intensifying the outflow southward to the Gulf of Mexico and eastward to the Atlantic. As a result of these seasonal alternations of temperature and pressure there is something of a monsoon tendency developed in the winds of the Mississippi Valley, southerly infiowing winds prevailing in summer and northerly outfiowing winds in winter; but the general tendency to inflow and outflow is greatly modified by the relief of the lands, to which we next turn.
In the low pressure two pipe system the flow pipe is carried to a sufficient height directly above the boiler to allow of its gradual fall to a little beyond the most distant point at which connexion is to be made with the return pipe, which thence slopes towards the boiler.
Iceland lies contiguous to that part of the north Atlantic in which the shifting areas of low pressure prevail, so that storms are frequent and the barometer is seldom firm.