Page:Popular Science Monthly Volume 34.djvu/148

138 irregular space. In one form, a light of from nine to eleven thousand candle-power, "actual," is obtained, which can only be compared with a conflagration. The size of the flame is so large that the shadows it casts are nebulous at the edges, and the volume of light so great that the shadows are partially illuminated by the reflections from surrounding objects, and the sharp contrasts and black shadows of the electric light are avoided. The same principle is adapted for heating purposes in the pyrigen, which gives a furnace free from sulphur, dust, and free oxygen, and of an absolutely steady temperature. The advantages are claimed for lucigen of low cost—it being one tenth that of gas-light of corresponding power—and extreme simplicity.

Fifty Tears of Sanitary Work.—The progress of sanitation in England during the fifty years of the Queen's reign has been reviewed by Captain Douglas Galton. Affairs were in a bad condition at the beginning of the history, in the absence of systematic methods of counteracting the natural accumulation and operation of propagating conditions of disease. Parochial administrations operated mischievously, in degrading the habitations of the working-classes and checking tendencies to improvement. The window-tax had been in operation one hundred and fifty years, to foster darkness and bar out ventilation. Water-supplies and the disposal of sewage had hardly been thought of, except in the larger towns. The first complete registration of vital statistics was made in 1838. A report of the Poor-Law Commissioners on sanitary conditions embodied many recommendations and principles that have since been recognized in legislation. It is now computed that by means of the measures that have been made effective, the annual saving of lives, over the previously prevailing death-rate, was, during 1860-'70, 4,064; during 1870-'80, 13,929; and from 1880 to 1884, 21,847. The whole death-rate for England and Wales has been reduced from 22·07 to 19·62 per 1,000; of deaths by zymotic diseases, from 4·52 to 2·71 per 1,000. The improvement in the last point in urban districts does not, however, appear to have kept pace with that in rural districts. The present social condition of the people affords other evidence of general improvement. The main feature of the legislation of the past half-century is the recognition of the principle that when large numbers are congregated in communities the duty of preventing injury from this aggregation rests on the community.

The Relation of Roots to Moisture.—Variations in plants are often produced by differences in conditions of the environment which are imperceptible to the observer; so that different plants, proceeding from seeds of the same pod and growing close together, are hardly ever precisely alike. Mr. H. Marshall Ward has shown how variations may be occasioned by conditions affecting the root. The active roots are furnished with fine hairs, which go out and draw in the moisture. The drier the soil and the more difficult to get moisture from it, the more thickly set generally are the hairs. The soil consists of innumerable fine particles, of different shapes, sizes, and composition, and each of these particles is covered with a thin layer of water, a water-blanket, which adheres to it tenaciously; although, when the moisture-coating exceeds a certain thickness, they will yield the surplus up quite readily. There are spaces between these particles, each enveloped in its water-blanket, and these interspaces influence the quantity of water which can be held back by the soil. If we can suppose a soil to be perfectly dry, the interspaces will be filled with air; when the soil is made moist, some of this air is driven out as the water comes in to take its place. If the soil is made excessively wet, all or nearly all the air may be driven out, though this seldom happens. The functions of the root-hairs are chiefly to apply themselves in the closest manner to the surfaces of the particles of the soil, so that the water attached to them can pass from the soil to the plant, and, with it, whatever dissolved matter it may contain. Some of this matter is oxygen dissolved from the air-bubbles, and this oxygen is essential to the life of the root-hairs. The effect of the deprival of oxygen is then gradually to cause the death of the root-hairs, then of the rootlets, the larger roots, and so on, till the whole plant perishes. This may take considerable time