508 



THE POPULAR SCIENCE MONTHLY. 



all instances it is essential that the land 

 should be well underdrained, and that the 

 sewage should all pass through the soil, 

 and not merely over it; otherwise, as has 

 been shown, it will only occasionally be sat- 

 isfactorily purified. The catch-water, or, 

 as the committee has termed it, the " super- 

 saturation" principle, is not defensible either 

 on agricultural, chemical, or sanitary prin- 

 ciples. An irrigation farm should therefore 

 carry out intermittent downward filtration 

 on a large scale, so that the sewage may be 

 always thoroughly purified, while at the 

 same time the maximum of utilization is 

 obtained. 



"It is certain that all kinds of crops 

 may be grown with sewage, so that the 

 farmer can grow such as he can best sell. 

 Nevertheless, the staple crops must be cat- 

 tle-food, with occasional crops of corn ; and 

 it is also certain, from the analysis of the 

 soil, that it has become very much richer, 

 and that the manurial constituents of the 

 sewage accumulate in it. Cattle should be 

 fed on the farm, which leads to a vast in- 

 crease in the production of meat and milk, 

 the great desiderata of the population pro- 

 ducing the sewage. Thus the system of 

 farming must be specialized and capital 

 concentrated, the absence of which condi- 

 tions has proved a great barrier to the sat- 

 isfactory practical solution of the sewage 

 question. 



"The committee has not been able to 

 trace any ill effects to the health of the 

 persons living around sewage farms, even 

 when badly conducted ; nor is there any 

 proof whatever that vegetables grown there- 

 on are in any way inferior to those grown 

 with other manure. On the contrary, there 

 is plenty of evidence that such vegetables 

 are perfectly suited for the food of man and 

 beast, and that the milk given by cows fed 

 on sewaged grass is perfectly wholesome ; 

 thus Mr. Dyke, Medical Officer of Health 

 of Merthyr Tydfil, states that, since the 

 abundant supply of milk from the cows fed 

 on irrigated grass, the children's mortality 

 has decreased from 48, 50, and 52 per cent. 

 of the total deaths, to only 39 per cent., 

 and that so far from diarrhoea having been 

 made more prevalent by the use of sewaged 

 cabbages, ' last year the Registrar-General 

 called attention to the fact that diarrhoea 



was less prevalent in Merthyr than in any 

 place in England and Wales ; ' and he ex- 

 pressed his belief in ' the perfect salubrity 

 of the vegetable food so grown.' 



" With regard to the assumption which 

 has been made that entozoic diseases would 

 be propagated by irrigation, all the evidence 

 that the country has been able to collect, 

 and more especially the positive facts ob- 

 tained by experiments, are against such an 

 idea ; and the committee is of opinion that 

 such disease will certainly not be more 

 readily propagated by sewage irrigation 

 than by the use of human refuse as manure 

 in any other way, and probably less if the 

 precaution be taken of not allowing the 

 animals to graze, but. always having the 

 grass cut and carried to them." 



Length of Thread of the Silk-worm.— 



Prof. Riley, of St. Louis, informs us that 

 the calculation, on page 663 of the last 

 volume, as to length of thread and weight 

 of cocoon spun by the mulberry silk-worm, 

 is altogether exaggerated. Instead of the 

 thread being 11 miles in length, it averages 

 not much more than half a mile, and seldom 

 exceeds 1,000 yards ; while a single mile, 

 instead of 28 miles of it, would weigh about 

 15£ grains. 



The Constitution of Carboniferous Strata. 



— ita general meeting of the British Asso- 

 ciation, Prof. W. 0. Williamson delivered 

 an interesting discourse on " Coal and Coal 

 Plants." The speaker said that most men 

 are now agreed as to the vegetable origin of 

 coal, and the drift theory of its accumula- 

 tion. It was once a vegetable soil, which 

 accumulated under the shade of primeval 

 forests, growing on areas of depression. In 

 time the land sank beneath the sea, and the 

 vegetable elements were buried under layers 

 of sand and mud, accumulations of which 

 again restored the area to the sea-level, 

 when spores of plants once more germi- 

 nated in a blue mud, and the succession of 

 phenomena which had previously occurred 

 was again renewed. The frequent repeti- 

 tion of these changes, finally, resulted in the 

 accumulation of the thousands of feet com- 

 posing the vertical series of rocks which are 

 termed the carboniferous strata. Attention 

 had been called by Prof. Huxley to some 



