138 



THE POPULAR SCIENCE MONTHLY. 



irregular space. In one form, a light of from 

 nine to eleven thousand candle-power, " act- 

 ual," is obtained, which can only be com- 

 pared 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 surround- 

 ing 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 tempera- 

 ture. The advantages are claimed for luci- 

 gen of low cost — it being one tenth that of 

 gas-light of corresponding power — and ex- 

 treme 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. Af- 

 fairs were ia a bad condition at the begin- 

 ning of the history, in the absence of sys- 

 tematic methods of counteracting the natural 

 accumulation and operation of projiagating 

 conditions of disease. Parochial adminis- 

 trations operated mischievously, in degrading 

 the habitations of the working-classes and 

 checking tendencies to improvement. The 

 window-tax had been in operation one hun- 

 dred 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 em- 

 bodied many recommendations and princi- 

 ples 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 doath-rate, was, 

 during 1860-'70, 4,064 ; during 18'70-'80, 

 13,929; and from 1880 to 1884, 21,847. 

 The whole death-rate for England and Wales 

 has been reduced from 22-OY to 1962 per 

 1,000 ; of deaths by zymotic diseases, from 

 4-52 to 2-'7l 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 evi- 

 dence 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 com- 

 munity. 



Tlje Relation of Roots to Moistnrc. — Va- 

 riations 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. Mar- 

 shall 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 dif- 

 ferent shapes, sizes, and composition, and 

 each of these particles is covered with a thin 

 layer of water, a water-blanket, which ad- 

 heres 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 them- 

 selves 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 



