156 



SCIENCE. 



[Vol. XI. No. 269 



which he brings out more clearly than any other writer with whose 

 works we are familiar, and to those we desire to call attention. 



In speaking of the London system, he pronounces it a failure. 

 This system he calls Bazalgettisni, from the distinguished engineer 

 who has applied it to London. Its essential principle is to discharge 

 either directly into an arm of the sea, or into a tidal river, at the 

 time of ebb-tide. Sewage matters discharged into the river at 

 Barking and Crossness are not pushed out to sea by the combined 

 action of the ebbing tide and current, as was expected, but mingle 

 with the water, and work their way back to points far above the 

 outfalls, thus effecting that pollution which the intercepting sewers 

 and the costly channels running parallel to the river were to have 

 averted. Mr. Slater summarizes the matter as follows : " The Bazal- 

 gette process, as applied to London, is a total failure. It involves 

 the utter waste of all the manurial matters in the sewage, it aids in 

 silting up the bed of the Thames, it occasions a nuisance much 

 complained of by the inhabitants of the country below the outfalls 

 on both banks, its cost is exceedingly serious, and it does not even 

 guarantee to the inhabitants of London an unpolluted river." It 

 would be hard to conceive of a more vigorous and thorough con- 

 demnation than this which Mr. Slater applies to the sewerage system 

 of London, and he is equally emphatic in reference to the proposed 

 extension of the system to Thames Haven at an expense of $20,- 

 000,000. 



The disposal of sewage by irrigation meets with no better 

 treatment at his hands. He asks, " Does irrigation effect its object 

 without occasioning annoyance or injury to the inhabitants of the 

 district .' " He has never failed to detect an unpleasant odor when 

 passing near an irrigation-field in warm, still weather. At Genne- 

 viUiers, near Paris, the odor on calm, autumnal evenings may, with- 

 out exaggeration, be described as abominable. Mr. Slater also 

 believes that irrigation-fields may produce actual disease in their 

 neighborhood, although he acknowledges that the evidence is some- 

 what conflicting. Irrigation does not remove germs, and it en- 

 courages flies, which act as carriers of these germs, it may be of 

 cholera or typhoid-fever. On this danger from flies the author is very 

 emphatic. He says that some of these insects that have become 

 saturated with putrescent matter, or actual disease-germs, enter 

 our houses and crawl over articles of food. Others settle upon our 

 persons, and inflict malignant wounds. Fatal illness has not un- 

 frequently been traced to the bite of flies which feed on sewage or 

 carrion. These flies being now recognized as among the greatest 

 agents for carrying putrid poisons and disease-germs to the healthy, 

 it is important that all places where they can increase and multiply, 

 and all matters upon which they may feed, should be made offen- 

 sive to them or destroyed, as the case may admit. 



These opinions are sustained by the experiments of Dr. Maddox, 

 published in the Journal of the Royal Microscopical Society, by 

 which it was demonstrated that the cholera bacillus can pass in a 

 living state through the digestive organs of flies, and also by the 

 experiment of Dr. Grassi, who showed that when segments of the 

 tape-worm ( Taenia solium) were placed in water, some of the eggs 

 remained suspended therein, and that in the intestines and excre- 

 ment of flies that drank of the fluid the eggs were subsequently 

 found. Observations made by other experimenters are also con- 

 firmatory of the fact that insects act as carriers of germs and ova 

 of parasites. Mr. Slater believes, too, that sewage-grass is very 

 inferior to normal herbage, and quotes experiments made by Mr. 

 Smee, and published by him in a work entitled ' Milk in Health 

 and Disease,' by which it was proven that milk from cows fed on 

 irrigation-grass became sour and underwent putrefaction much soon- 

 er than that from cows fed on grass from an ordinary meadow. 



In concluding the discussion of irrigation, the author says that 

 irrigation, though an excellent method of disposing of, and at the 

 same time utilizing sewage, when suitable land is available, where 

 the climate is warm, and the rainfall scanty or intermittent, is 

 not applicable where these conditions are absent. Any attempt to 

 represent it as the only means of dealing with the sewage difficulty, 

 and to force it upon reluctant communities, is a grave error ; in 

 fact, a crime, the motives for which are in most cases hard to trace. 

 The methods of sewage-disposal by filtration, precipitation, de- 

 struction, distillation, and freezing, are described, and their advan- 

 tages and disadvantages pointed out. 



The author, in concluding his treatise, devotes more than sixty 

 pages to giving an abstract of the specifications of the 454 patents for 

 the chemical treatment of sewage, occasionally adding a note point- 

 ing out what he considers to be their defects. 



Letters of David Ricardo to Thomas Robert Malthus. Ed. by 

 James Bonar. Oxford, Clarendon Pr. 8". S2.75. 



The letters in this collection were written between 1810 and 

 1823, the last of the series being dated only a few days before the 

 writer's death. They are only in a minor degree personal, being 

 mainly devoted to discussing the many questions in political 

 economy on which Ricardo and Malthus disagreed. Unfortunately, 

 the letters that Malthus wrote to Ricardo have never been found ; 

 so that we have only one side of the discussion, which is a draw- 

 back both to the interest and to the instructiveness of the corre- 

 spondence. It is true that Ricardo often states his opponent's 

 arguments ; but such statements cannot supply the place of Mal- 

 thus' own words. However, the letters will be very interesting to 

 students of economics, illustrating as they do the views of two of 

 the principal founders of the science. The men were personal 

 friends, and were often in each other's company; but on economic 

 themes they differed widely. They agreed in the 'main on the sub- 

 jects of rent and population ; but they disagreed on many matters 

 of detail and on some of prime importance. Thus, they differed 

 widely as to the definition of value, and as to the influence of sup- 

 ply and demand on the one hand, and of cost of production on the 

 other, in determining value. They also differed as to the real 

 nature of political economy ; Malthus holding that it is an inquiry 

 into the nature and causes of wealth, while Ricardo would confine 

 it to the subject of distribution only (p. 175). 



The two leading faults in Ricardo's published works appear with 

 equal plainness in these letters. The first of these is his habit of 

 fixing on one or two economic laws or forces, and tracing out their 

 results without regard to the minor influences which often modify 

 their action. He seems to have been aware himself of this ten- 

 dency in his thinking ; for he remarks in one of his letters that one 

 of the chief causes of the differences between himself and Malthus 

 was that he looked only to the larger and more permanent causes, 

 while his opponent was always thinking of the minor ones. On 

 this point, as on some others, it would have been well if the two 

 friends had been content to learn from each other. The other de- 

 fect in Ricardo's theories to which we have alluded is his constant 

 assumption that wages are always at the starvation point, so 

 that the slightest increase in the cost of living will necessitate a 

 rise of wages in order that the supply of labor may be kept 

 up. Thus, he argues that a tax on breadstuffs would lead to a rise 

 in wages, and consequent fall in profits ; whereas it might only re- 

 sult in reducing the standard of living among the laborers, so that 

 the whole burden would fall upon them. 



The friendship between the two correspondents, notwithstanding 

 their difference of opinion, was of the warmest character, as is 

 proved by many passages in these letters, and also by a remark 

 made by Malthus after Ricardo's death, and quoted at the end of 

 this volume. He said, " I never loved anybody out of my own 

 family so much. Our interchange of opinions was so unreserved, 

 and the object after which we were both inquiring was so entirely 

 the truth and nothing else, that I cannot but think we sooner or 

 later must have agreed." We should add, that the book is well 

 edited, and that it contains much information, both in the text and 

 in the notes, about Ricardo and Malthus themselves, and also about 

 other political economists who lived in their time, so that it has a 

 biographical as well as a scientific interest. 



Lectures on Electricity. By GEORGE FORBES. London and 

 New York, Longmans, Green, & Co. 12". $1.50. 



A NUMBER of popular works on electricity have been published in 

 the last few years. Some are clearly written, some are interesting, 

 very few are calculated to give correct ideas of the broad principles 

 of the science of electricity. 



There are six lectures in Professor Forbes's book, " intended for 

 an intelligent audience, ignorant of electrical science, but anxious to 

 obtain sufficient knowledge of the subject to be able to follow the 

 progress now being made in the science." For its purpose the book 

 IS admirable. The simpler phenomena — if we may consider any 



