Various conjectures have been formed by naturalists, concerning the origin of springs; but, consistently with our limits, we shall only observe, that the most plausible theory appears to be that of Dr. Halley, who supposes them to originate from the rain and snow waters; which, penetrating through the soil, at length settle in the fissures of the earth, and form fountains or springs.
As water is indispensable to the health and convenience of mankind, many expedients have been devised, with a view to ascertain the particular spots, whence a supply might be obtained : we shall, therefore, state a few indications, or land-marks, by which that necessary article may be discovered.
1. As all mountains are colder in proportion to their height, the evening mist descends on them, particularly in damp situations, much sooner than on the vallies, and thus may indicate the existence of springs.
2. Another observation is suggested by Dr. Darwin, in order to determine the existence of subterraneous springs, in rimy mornings : - moist earth conducting heat better than dry soil, the rime will be dissolved more speedily on those spots which are moistened by springs under ground, than on the adjacent parts.
Lastly, the rise of these natural fountains may be discovered during the winter, in wet ditches, by growing of brook-lime, water-cresses, or similar aquatic plants : for such vegeables do not thrive in the ditches that become dry in the summer. And Dr. Darwin remarks, that when those ditches which contain springs, are nearly dry, the direction of the current may be ascertained by the point, which the leaves of the aquatic plants may turn, with as great a degree of certainty as can be ef-fected by a level.