June i, 1893] 



NA TURE 



i'7 



thought Mr. Boys' method would supplant the laborious pro- 

 cesses now used to determine the paths of projectiles. Where 

 the resistance varied as the square of the velocity the elevation 

 for maximum range depended on the initial velocity, and for a 

 cube law both elevation and range tend to finite limits as the 

 initial velocity increases. Prof. Minchin inquired whether the 

 catenary could be best drawn by using a scale of equal parts 

 instead of one divided reciprocally. The President greatly 

 appreciated the saving of labour effected by Mr. Hoys' method, 

 and thought the apparatus should be shown at the forthcom- 

 ing exhibition of mathematical instruments in Germany. — 

 Prof. O. J. Lodge, F. R. S., read a paper on the foundation 

 of dynamics, in which he examines the objections raised by 

 Dr. MacGregor [Phil. Mag., Feb. 1893) against the views of 

 Newton's Laws of Motion and the Conservation of Energy, ex- 

 pressed by the author in 1885. The first part of the paper 

 treats of the nature of axioms. An axiom or fundamental law 

 is regarded as a simple statement suggested by familiar or easily 

 ascertained facts, probable in itself, readily grasped, and not dis- 

 proved or apparently liable to disproof, throughout a long course 

 of experience. On such bases the conservation of energy and of 

 matter rests. Neither can be proved generally, but like other 

 fundamental laws they fit into a coherent and self-consistent 

 scheme, and are therefore worthy of acceptance until they are 

 shown to be wrong. The second part relates to the first and 

 third laws of motion. Dr. MacGregor objects to the first law 

 on the ground that uniform motion is unintelligible unless its 

 direction and velocity are specified with reference to a set of 

 axes, and directly axes are introduced, difficulties occur as to 

 their motion, because there is no satisfactory criterion of rest. 

 Such notions the author deems artificial and unnecessary, ex- 

 cept where it is required to define the absolute magnitude and 

 direction of the motion. Reasoning from his own experiments, 

 he believed the ether was at rest, for he had not found it pos- 

 sible to move it by matter. The first law, he said, had been 

 considered unnecessary, as being only a particular case of the 

 second. While admitting the latter fact, he maintained that its 

 separate statement was desirable, on account of its simplicity, 

 and its affording a practical definition of the mode of measuring 

 time. As regards the third law being deducible from the first, 

 he pointed out that if it could be axiomatically asserted that 

 the centre of mass of a rigid system moves uniformly unless an 

 external force acts on the system, then the third law follows. 

 Newton apparently considered it best to state the third law as 

 an axiom, but to many persons it is not obviously axiomatic 

 (some engineers do not accept it), hence its deduction from the 

 other two laws is useful. Part IIL of the paper deals with the 

 deduction of the law of conservation of energy from Newton's 

 third law, and universal contact-action. Dr. MacGregor objects 

 to the author's definition of energy as the name given to " work 

 done," and contends that this definition assumes conservation. 

 On this point Dr. J^odge invited criticism, meanwhile pointing 

 out that his definition was analogous to the customary definition 

 of the potential function, and a name for the line integral of a 

 force considered as a quantity that can be stored. On the 

 basis taken, two bodies can only act on one another whilst in 

 contact, hence, if they move, they must move over equal dis- 

 ances ; but their action consists of a pair of equal and opposite 

 forces, therefore their activities are equal, and whatever energy 

 one loses the other gains, i.e., energy is transferred from one 

 body to another without change in quantity. In Part IV. the 

 dissipation of energy, the nature of potential energy, and the 

 second law of thermodynamics, are considered. In discuss- 

 ing transference and transformation, " potential energy" is used 

 to indicate the energy of a body under stress, and "kinetic 

 energy," that due to sustained motion. Each corresponds to 

 one of the factors of the product Vv, "activity." So long as 

 one factor is absent no activity can manifest itself, but directly 

 the missing factor is supplied, transference and transformation 

 begin. This was shown to hold in an example of an air-gun 

 with its muzzle plugged, chosen by Prof. MacGregor as an 

 instance of transference of potential energy without transforma- 

 tion. The law of dissipation of energy is stated thus : — " If a 

 body has any portion of energy in such a condition that it is 

 able automatically to leave the body, that portion usually does 

 so sooner or later." Instead of the ordinary form of the second 

 law of thermodynamics the following statement is proposed : — 

 "The portion of energy which a body can automatically part 

 with is alone available for doing work." In discussing this 

 subject the author points out that the common notion that heat 



NO. I 23 I, VOL. 48] 



engines are much less efficient than water or electric engines is 

 a mistake, arising from the fact that in the one case the effici- 

 ency is calculated on the total energy, whilst in the latter cases 

 only the available energy is considered. Two appendices 

 accompany the paper, one the objectivity of energy and the 

 question of gravitation, and the other on more detailed dis- 

 cussion of the transmission of energy in difficult cases. 



Chemical Society, May 4. — Dr. Armstrong, President, in 

 the chair. — The following papers were read : — The hydrates of 

 sodium, potassium and lithium hydroxides, by S. U. Picker- 

 ing. By cooling solutions of sodium hydroxide, the author has 

 succeeded in isolating a number of crystalline hydrates ; their 

 formulae and freezing-points are given in the following table : — 



The hydrate containing 3J molecules of water is the only one of 

 the eight which has been previously described. In the case of 

 potassium hydroxide two new hydrates have been isolated ; 

 these have the formula; K0II,H20 and KOH,4H20, and 

 freeze at 143° and -327° respectively. The previously known 

 dihydrate freezes at 35 '5°. Lithium hydroxide monohydrate, 

 which was already known, was the only hydrate of this hy- 

 droxide isolated. — Detection of arsenic in alkaline solution, by 

 J. Clark. Arsenic acid is not reduced to hydrogen arsenide by 

 zinc dust and caustic potash, or even by sodium amalgam in 

 alkaline solution. No trace of arsenic volatilises on heating 

 sodium arsenate with a large excess of aluminium and caustic 

 soda. The statement of H. Fresenius, that Gatehouse's 

 modification of Fleitmann's test indicates arsenic acid, is hence 

 erroneous ; Fresenius's results are probably due to the use of 

 impure aluminium or of arsenic acid containing arsenious acid. 

 The author concludes that none of the methods hitherto pro- 

 posed for the generation of hydrogen arsenide from alkaline 

 solutions, are available for the detection of arsenic acid. — Im- 

 provements in Reinsch's process, by J. Clark. Although 

 Reinsch's process is sensitive to minute quantities of arsenic, 

 and removes all traces of that element from organic mixtures, 

 there are two objections to its use in medico-legal cases. With 

 small quantities of arsenic, the stain obtained is sometimes not 

 easily identified, as the coated copper when heated is apt to 

 give a sublimate of cupric chloride and organic matter instead of 

 arsenious oxide ; the method is also not suitable for quantitative 

 estimations, as the whole of the arsenic cannot be volatilised 

 from the copper by means of heat. The author's improvement 

 on Reinsch's process consists in digesting the coated copper 

 with cold caustic potash and hydrogen peroxide, and dis- 

 tilling with ferrous chloride and hydrochloric acid. The 

 arsenic is precipitated in the distillate and weighed as sulphide, 

 whilst any antimony present may be detected in the residual 

 liquor. — The action of light in preventing putrefactive decom- 

 position and in inducing the formation of hydrogen peroxide in 

 organic liquids, by A. Richardson. Several observers have 

 noted that the development of putrefactive organisms is checked 

 by the combined action of sunlight and oxygen ; this sterilising 

 influence of light in presence of oxygen has apparently always 

 been regarded as the outcome of an action exerted by the 

 organism. The author has made a number of experiments with 

 urine, in order to ascertain whether, when sterilisation has been 

 effected by light, any oxidising agent, such as hydrogen peroxide, 

 is formed, and whether such substance may not be the sterilis- 

 ing agent. No hydrogen peroxide is produced by the action of 

 oxygen on sterilised urine in the dark, but an appreciable amount 

 of the peroxide is formed on exposing such urine to light ; the 

 production of the peroxide is hence independent of the presence 

 of organisms. Substances, such as manganese dioxide, which 

 destroy hydrogen peroxide, greatly facilitate organic growth; 

 the addition of hydrogen peroxide to fresh urine renders 

 the liquid much less liable to change under the influence of or- 

 ganisms, whilst if added to urine in which fermentation has 

 already set in, the peroxide is rapidly decomposed. — The sup- 

 posed saponification of linseed oil by Dutch white lead, by J. B. 

 Ilannay and A. E. Leighton. The author shows that the state- 



