But what harm does evaporation do? and what has all this scientific talk to do with drainage? These, my friend, are very practical questions, and just the ones which it is proposed to answer; but we must bear in mind that, as Nature conducts her grand affairs by systematic laws, the small portion of her domain which for a brief space of time we occupy, is not exempted from their operation. Some of these laws we may comprehend, and turn our knowledge of them to practical account. Of others, we may note the results, without apprehending the reasons of them; for it is true-- "There are more things in Heaven and earth, Horatio, Than are dreamt of in your philosophy." Discussions of this kind may seem dry, though the subject itself be moisture. They belong, certainly, to the topic under consideration. Evaporation does harm in the Spring-time, because it produces cold, just when we most want heat. How it produces cold, is not so readily explained. The fact may be made as evident as the existence of sin in the world, and, possibly, the reason of it may be as unsatisfactory. The books say, that heat always disappears when a solid body becomes a liquid; and so it is, that the air always remains cool while the snow and ice are melting in Spring. Again, it is said that heat always disappears, when a fluid becomes vapor. These are said to be laws or principles of nature, and are said to explain other phenomena. To a practical mind, it is perhaps just as satisfactory to say that evaporation produces cold, as to state the principle or law in the language of science. That the fact is so, may be proved by many illustrations. Stockhardt gives the following experiment, which is strikingly appropriate: "Fill a tube half full of water, and fasten securely round the bulb of it, a piece of cloth. Saturate the cloth with cold water, and then twirl the tube rapidly between the hands; presently the water in the tube will become sensibly colder, and the degree of cold may be accurately determined by the thermometer. Moisten the cloth with ether, a very volatile liquid, and twirl it again in the same manner as before; by which means, its contents, even in Summer, may be converted into ice."