British Rainfall 1867, p.9
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British Rainfall 1867 page 9
objects, near the residences of the various observers. Lastly, it has for some years been my constant habit to take a series of aneroid observations whenever travelling by road or rail; and thus fair approximations to the altitude of some hundreds of railway stations have been obtained. Glad as I am to see the altitude column steadily filling, I wish to feel more certain of the correctness of these values, and also to sweep away the numerous queries which exist in that column. Towards effecting this, I renew an offer previously made, viz.:- "We can only say that, any of our readers who are uncertain of their altitude, and will send us the position of their houses in the following form,- "The Limes, Johnstone, Derbyshire, "Quarter of a mile South of Johnstone Church, "shall be assisted to the best of our power." In all except mountainous districts, the amount of rain collected increases about 2 1/2 per cent. per 100 feet of increased elevation; therefore it is evident that in the greater part of England an error of 50 ft. in the height above sea involves an error in the amount of rain indicated of (30in. ÷ 100 x 1.25 =0.38) about four-tenths of an inch. EVAPORATORS AND EVAPORATION. THE Astronomer Royal at the Manchester meeting of the British Association described meteorology as one of the most desperate sciences with which we have to do. I almost think the most desperate branch of this desperate science is evaporation. Prima facie, it seems simple enough to ascertain how much water is taken from the earth's surface; but a little consideration will show that it must vary with (1) the nature of the soil and subsoil; (2) the inclination of the ground; (3) the aspect of the ground; (4) the presence, or otherwise, of vegetation; (5) the nature of the vegetation (some plants give off twice the moisture others do); (6) almost every variation of climate; certainly temperature, humidity, rain, wind, sunshine, and cloud; (7) I would add the physical characteristics of the district, proximity to sea, and altitude, but that their effects ought to be detected by a strict knowledge of the meteorology of the district, implied by condition (6). How many of these requirements are fulfilled by a few pints of water in a metal vessel four or five feet above the ground? Yet this is the almost universal method of determining the amount of evaporation. Was I not justified (page 43) in saying, "I don't believe in evaporators." My friend, Mr. Fletcher him |
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