igS 



NA TURE 



[Jan. 15. 1874 



(similar to the Inspectors under the Alkali Act) should be 

 appointed, to whom should be committed the duty of 

 detecting and proving offences against the law, and of 

 procuring the conviction of offenders. They consider 

 that the formation of River Conservancy Boards for 

 authorising and carrying out river improvements will in 

 course of time become imperative, but they are convinced 

 that the thing of immediate importance in connection with 

 river improvement throughout the country, is simply the 

 prohibition, under adequate penalties, of the gross 

 pollution which at present renders so much of the running 

 water of this country useless to manufacturers, agri- 

 culturists, and the like. 



The time has nntyet arrived forthe full discussion of these 

 proposals. We shall doubtless hear much on this subject in 

 the approaching or in the next session in parliament. It is, 

 however, certain, from the opposition made to the bill of 

 last year, that manufacturers do not as a rule agree with 

 the Commissioners as to the feasibility of enforcing the 

 proposed standards of purity, as regards the effluent 

 water from works of various kinds. Nor is public 

 opinion respecting the other and far more important 

 iource of pollution, the sewage of towns, in a sufficiently 

 advanced or satisfactory condition to render legislation 

 easy. It is not, for instance, clear how one and the same 

 system, say of irrigation, can be applied to all districts 

 possessing different soils, rainfalls and situations. In- 

 deed, the more we consider the whole question of the 

 prevention of the pollution of rivers, the more difficult 

 does any general method of treatment appear to be. Each 

 locality has its own peculiarities, and a system of preven- 

 tion which is suited to one district may be inapplicable or 

 inexpedient in another. But even supposing that when the 

 subject comes before Parliament that difficulties are 

 found to be of such a character as to render it impossible 

 to legislate upon the exact basis laid down by the Com- 

 missioners, still the value of their conclusions, and of 

 the mass of experimental evidence which they have col- 

 lected, is extreme • and they have m.ost fully earned the 

 gratitude of all those, interested in the satisfactory solu- 

 tion of one of the most important, though most difficult, 

 questions of our social economy. 



THE CONSERVATION OF ENERGY 



All Elementary Treatise on Energy and its Laws. By 

 Balfour Stewart, M.A., LL.D., F.R.S., Professor of 

 Natural Philosophy at the Owens College, Manchester. 

 (Henry S. King & Co., 1873.) 



IT is the proper function of Science to discover, among 

 the ever-changing phenomena of the world, the 

 permanent relations which are the conditions of reason- 

 able thought. When we understand these relations well 

 enough to express them in words we call them " Laws of 

 Nature." When they rise to a higher stage of develop- 

 ment and have become invariable habits of thought, we 

 call them " Things." 



Thus ice, under certain conditions, ceases to be ice. 

 We observe that when the ice melts water appears in its 

 place, and we find that there is always so much water in 

 place of so much ice. We therefore obtain, in the first 

 instance, a /aw of equivalence between a certain quantity 



of ice and a certain quantity of water, and finally, we 

 arrive at the conclusion that water and ice are the same 

 thing in different forms. 



Wc afe thus led to inquire what it is which remains 

 permanent in the midst of all apparent changes, and the 

 result of this inquiry has been the enunciation of a con- 

 sistent definition of the quantity of matter in a body, and 

 the establishment of the doctrine that the quantity of 

 matter in a body is invariable, whatever transformations 

 it may undergo. 



This doctrine of the " Conservation of Matter" lies at 

 the foundation of all reasoning, whether in physics or in 

 chemistry. When the progress of Science rendered it 

 possible to form exact ideas about the motion of bodies, 

 men were again impelled to seek for something perma- 

 nent, even in motion itself. They endeavoured to form 

 some definition of the " Quantity of Motion " which should 

 enable them to treat this quantity as a thing having a 

 continuous existence. The long war between the followers 

 of Newton and those of Leibniz as to whether, in estima- 

 ting the quantity of motion, the mass must be multiplied 

 into the velocity or into the square of the velocity, was 

 not a mere debate about words and names, for it involved 

 the question whether momentum or vis viva were the 

 more fully possessed of that character of permanence 

 which would justify its claim to the title of "The Quantity 

 of Motion." 



The doctrine of the Conservation of Energy is the most 

 complete expression hitherto given to the belief that all 

 the changes of phenomena are but different distributions 

 of the same stock of energy, the total quantity of which 

 remains invariable. The characteristic feature of scientific 

 progress during the last thirty years has been the appli- 

 cation of principles derived from this doctrine to the 

 various branches of Science. The recent progress of the 

 theory of heat is an instance of the direct and conscious 

 application of the doctrine of the conservation of energy. 

 In his electrical discoveries Faraday also was guided by 

 the same doctrine, though less consciously, as he had no 

 opportunity of becoming acquainted with it in the accurate 

 form in which it may now be stated. 



In the volume before us Dr. Balfour Stewart has 

 explained, in a very clear and very elementary manner, 

 what is meant by energy in its two forms, the energy of a 

 moving system, and the energy due to the configuration 

 of the system. 



This exposition is so carefully drawn up that we think it 

 ought to be intelligible even to students who approach the 

 subject without any previous training in the technical dy- 

 namics of the ordinary text-books. This we consider a 

 matter of great moment for the future progress of Science. 

 It is no doubt easier, in dealing with the j^resent genera- 

 tion of students, to gain their assent to doctrines about 

 energy by deducing them from other principles which 

 have been already taught them as the elementary prin- 

 ciples of dynamics. But it is by no means always true 

 in science that those principles' which have been longest 

 recognised are really the most elementary. The discovery 

 of principles more fundamental and elementary than those 

 which ai-e already received, is not only of great importance 

 in the philosophy of Science, but it tends to render Science 

 less technical, and therefore more easily diffusible through 

 the mass of society. 



