Lectures, reports, letters, and papers on sanitary questions / by Robert Rawlinson.

  • Rawlinson, Robert.
Date:
1876
Catalogue details

Licence: Public Domain Mark

Credit: Lectures, reports, letters, and papers on sanitary questions / by Robert Rawlinson. Source: Wellcome Collection.

    10/164 page 4
    former; and, in combination with these two gases there also exists a fractional per centage of carbonic acid gas. In this atmosphere water is present in the form of vapour.* The one main source of heat to the surface of the earth and atmosphere, and of electric action, is the sun. By the action of the sun, also, is produced all those phenomena of Meteorology which we have to consider. That great reservoir of water, the salt ocean, is the prime source of all ‘‘fresh water,’ wherever and however it may be present, either upon the surface of the land, or within the stratafied crust of the globe. And it is through the process of evaporation that all ‘‘sweet” or ‘‘fresh water” is obtained from the salt waters of the ocean. If the heat emitted from the sun were, year by year, uniformly the same, there would, necessarily, be uniformity of evaporation ; and this would imply a corresponding annual uniformity in precipitation of vapour in the form of dew, snow, hail, or rain. On the other hand, the reverse of these statements will be equally true: that is to say, irregularity in the emission of heat from the sun must be attended with a corresponding irregularity in the volume of ocean-water evaporated, which last irregularity must also in the same degree affect the volume of fresh water obtained by precipitation. Whether the heat of the sun, year by year, be uniform, or whether it is subject to fluctuating variations, it may be assumed as certain, that the heat-giving action only varies within certain limits, and so conforms to every other known operation of nature; for we observe the grand phenomena of the elements obeying a law which, out of apparent irregularity and inequality, brings forth equality and order, just as a pendu- lum ever beats true time in its swing, however great or however slight may be its motion; such variety pervades nature’s working, and such is the type of variety in the transmission of solar heat to this earth ; that so, in a series of years, an average temperature is determinable, to which may be referred all those complex and won- derful changes that are perpetually taking place on the surface of the globe. j The leading facts to be recognised by engineers are con- sequently these: there is evaporation from the ocean caused by the heat of the sun; and in proportion to this heat is the volume of water that in each year is evaporated; this vapour, whatever its volume carried into the atmosphere, must again be precipitated in the form of fresh-water. These grand evolutions of the elements can be brought under no control by human power. Experience has demonstrated that in different countries and climates the annual volume of rain which falls is subject to con- * The permanent gases of the atmosphere are nitrogen, oxygen, and carbonic acid. The first two are always found in nearly unvarying proportion of 80 per cent. of nitrogen and 20 per cent. of oxygen, with carbonic acid in a fractional proportion—from 3:7 to 6°2 in 10,000 parts.
    digitised image 1
    digitised image 2
    digitised image 3