these mills require little or no attention, and work at all times when the wind blows. When water accumulates in valleys lying above the sea, deep cuttings or even tunnels may be necessary to carry off the water; at Neufchâtel in Switzerland, very extensive tracts of land have been reclaimed, by boring a tunnel through the surrounding hills, and thus letting off the water from the lakes formed by the rain. Sometimes land may be drained by boring through the clay or other impervious soil, down to a porous stratum, such as sand or gravel. A knowledge of the structure of the whole district is necessary to determine whether this is likely to be of service or not. By boring deep pits in the drains cut in peat mosses, the weight of the mosses will cause the water to be squeezed out, which rising in these holes flows off by the drain, producing the same effect as if it were cut to the depth of the pits. Drains are frequently made by means of narrow curved spades, but the draining plough effects the purpose more rapidly, and is very generally used. The drainage of London and other large towns consists of small drains from each house, made of earthenware tubes leading to a sewer of brickwork, running along each street and uniting with larger ones. The question of effectually draining London is a very difficult one, schemes of various kinds being at this time propounded, which would cost several millions of pounds to put into practice; at present all the sewage runs into the river Thames, and it is a matter of serious importance to obviate this, by carrying it off to some other place. ARTESIAN WELLS. Illustration: FIG. 1. (‡ BENT TUBE.) Illustration: FIG. 2. (‡ TAPPED BENT TUBE.) Illustration: FIG. 3. (‡ ARTESIAN BASIN.) Illustration: FIG. 4. (‡ DRILL BIT.)