To take a familiar instance: it is but recently that attention has been drawn to the great influence of slight differences in station upon the results of observations of temperature and precipitation. Two thermometers hung but a few hundred yards from each other differ not unfrequently five, sometimes even ten degrees in their readings; [Footnote: Tyndall, in a lecture on Radiation, expresses the opinion that from ten to fifteen per cent. of the heat radiated from the earth is absorbed by aqueous vapor within ten feet of the earth's surface.--Fragments of Science, 3d edition, London, 1871, p. 203. Thermometers at most meteorological stations, when not suspended at points regulated by the mere personal convenience of the observer, are hung from 20 to 40 feet above the ground. In such positions they are less exposed to disturbance from the action of surrounding bodies than at a lower level, and their indications are consequently more uniform; but according to Tyndall's views they do not mark the temperature of the atmospheric stratum in which nearly all the vegetables useful to man, except forest trees, bud and blossom and ripen, and in which a vast majority of the ordinary operations of material life are performed. They give the rise and fall of the mercury at heights arbitrarily taken, without reference to the relations of temperature to human interests, or to any other scientific consideration than a somewhat less liability to accidental disturbance.] and when we are told that the annual fall of rain on the roof of the observatory at Paris is two inches less than on the ground by the side of it, we may see that the height of the rain-gauge above the earth is a point of much consequence in making estimates from its measurements. [Footnote: Careful observations by the late lamented Dallas Bache appeared to show that there is no such difference in the quantity of precipitation falling at slightly different levels as has been generally supposed. The apparent difference was ascribed by Prof. Bache to the irregular distribution of the drops of rain and flakes of snow, exposed, as they are, to local disturbances by the currents of air around the corners of buildings or other accidents of the surface. This consideration much increases the importance of great care in the selection of positions for rain-gauges. But Mr. Bache's conclusions seem not to be accepted by late experimenters in England. See Quarterly Journal of Science for January, 1871, p. 123.]