1 66 



NA TURE 



[June 15, 1893 



pounds all terminate somewhere about the strongest series of 

 water vapour lines in the ultraviolet. Typical non-metallic 

 spectra are sulphur, selenium, and tellurium ; the first yields a 

 continuous spectrum with a series of beautiful fluted bands, the 

 second a series of fine bands, occurring at closer intervals, and 

 the third is characterised by bands still closer together and near 

 the more refrangible termination of which four lines occurring 

 in Hartley and Adeney's spark spectrum of tellurium are visible. 

 Increase in atomic mass causes shorter periods of recurrence of 

 bands. In line spectra it is the reverse ; increase in atomic 

 mass causes greater periods in the recurrence of lines. Charcoal 

 and carbon monoxide yield chiefly continuous spectra ; the 

 latter, however, exhibits some carbon lines. The hydrocarbons 

 yield the well-known spectrum of carbon bands with also those 

 attributed to cyanogen. Of metallic elements, nickel, chromium, 

 and cobalt yield purely line spectra ; antimony, bismuth, silver, 

 tin, lead, and gold beautiful banded spectra (spectra of the first 

 ordei) accompanied by some few lines. 



Iron and copper exhibit lines, and, less prominently, bands. 

 Manganese has a beautiful series of bands and a group of three 

 very closely adjacent lines. Aluminium gives a fine continuous 

 spectrum with three lines, origin uncertain, zinc a continuous 

 spectrum without lines, and cadmium a spectrum consisting of 

 one single line only, \ 326o'2. 



Of compounds, chromic trioxide yields a continuous spectrum 

 with six lines belonging to the metal, copper oxide a fine band 

 spectrum with two lines of the metal, magnesium sulphate gives 

 a spectrum of magnesium oxide consisting of broad degraded 

 bands composed of closely adjacent fine lines and one line be- 

 longing to the metal, K 2852. 



The sulphates of calcium, strontium, and barium give both 

 bands of the oxides and lines of the elements. Phosphorus 

 pentoxide yields a continuous spectrum with one peculiar line, 

 seen also in the spectrum of arsenic. 



The chlorides of the alkali metals give also lines of the ele- 

 ments with a more or less continuous spectrum, which, it i? 

 believed, is due to the metal in each case. Lithium chloride 

 gives no continuous spectrum. 



The Volatility of Metals. — One of the most interesting facts 

 ascertained by this investigation is the volatility of all the 

 metals examined, except platinum, and particularly the extra- 

 ordinary volatility of manganese, and, to some extent, of the 

 infusible metal iridium. Metal believed to be pure iridium is 

 seen to have diminished after the flj.me has played upon it for 

 about two hours. 



Physical Society, May 26, Prof. A. W. Riicker, F.R.S., 

 President, in the chair. — Mr. C. J. Woodward showed some 

 experiments with a vibrating bar. On suspending the bar by 

 two loops of cord, and placing it over a resonance box, the 

 sound was greatly intensified. When placed crosswise, and 

 partly over the box, a position could be found where no in- 

 crease of sound resulted, whilst a little movement in either 

 direction from this position caused a considerable increase. — The 

 discussion on Dr. Lodge's paper, the foundation of dynamics, 

 was then resumed. Communications on the subject Irom Mr. 

 S. H. Burbury, Dr. G. Johnstone Stoney, and Prof. E. F. 

 Herroun were read. Prof. Minchin said the first fundamental 

 axiom of dynamics postulates the existence o( Force ?ls an entity 

 distinct from Mattir, Space, and Time^ and this was the object 

 of Newton's First Law. It also gave the criterion of (he 

 presence of force. To merely retain the law as defining equal 

 times was to degrade it. As regards the supposed impossibility 

 of defining uniform motion he said, similar difiiculties occur in 

 all sciences, even in geometry. Nevertheless a rational science 

 of geometry existed. In dynamics we had notions of a right 

 line and of uniform motion in it, although no criterion of either 

 may exist. The fact that the science harmonises with ordinary 

 experience constitutes its validity. In his opinion the extra- 

 ordinary devices which had been suggested for defining 

 directions fixed in space were unnecessary, and merely served to 

 cover the subject with ridicule. He disagreed with Prof. 

 Lodge in admitting the first law as a particular case of the 

 second, for unless force was postulated (the function of the first 

 law), the second became a mere definition, and not a law. 

 Speaking of the third law he said the author had made a serious 

 error in stating that it could be deduced from the first, for the 

 centre of mass of a system might be at rest, without action and 

 reaction necessarily beir.g equal and opposite. The third law 

 was not superfluous ; neglecting it had led to great miscon- 

 ception and mystery about the Principle of Virtual Work, and 



NO. 1233, VOL. 48] 



D'Alembert's Principle, both of which are simple deductions 

 from it. In opposition to Dr. Lodge, he defended the ordinary 

 definition of Energy, and asserted that without the notions of 

 force and ivork, the term energy loses all meaning. Speaking 

 of transference and transformation of energy, he inquired if the 

 proof given could be applied to the case of a body sliding down 

 a rough rigid inclined plane, for here the stress (friction) does 

 work on the body but not on the plane, and there was no trans- 

 ference. He regretted that the expression "potential energy" 

 was used in dififerent senses in the paper, sometimes meaning 

 "static energy," and at others "the available portion of the 

 kinetic energy of a body," Referring to the idea of all energy 

 being ultimately kinetic, he asked if by accepting this the 

 author meant to surrender the independent existence of force. 

 If so, difficulties would arise ; for example, in the kinetic theory 

 of gases the expression for the pressure, / = J p v"-, was only 

 arrived at by assuming the existence of force. The statement 

 on t'he top of slip 9 about making a "moving body do 

 work " was not necessarily true, as might be seen by considering 

 the case of a sphere rolling down a rough inclined plane. 

 Prof. O. Henrici thought axioms should be treated as true 

 logical definitions, as for example in geometry, "two straight 

 lines cannot enclose a space." Every new notion required its 

 axiom. In passing from geometry to kinematics the idea of 

 Time presented itself, and the appropriate axiom was contained 

 in Newton's first law. On approaching dynamics Force and 

 Mass were met with. He disagreed with Prof. Minchin in re- 

 garding force as most fundamental. Mass was more essential, 

 for force might be abolished. On the other hand, he concurred 

 with Prof. Minchin in thinking that the idea of a centre cf mass 

 was not axiomatic. Referring to Dr. Lodge's summary 

 (Natuke, p. 62) he agreed with axiom (a) fully, and 

 with {/>) partially. Axiom 3 required further development. 

 The crucial point, however, was axiom 4, "Stress cannot exist 

 in or across empty space." This he regarded as very incom- 

 plete, and maintained that axioms defining the properties of the 

 ether were necessary to further progress. If varieties of space 

 be contemplated each advance required ftesh axioms. Dr. C. V. 

 Burton remarked that contact movement did not necessitate 

 equal velocities ; sliding motion was a case in point. Again, 

 in deforming an incompressible fluid, although force and motion 

 might exist, no work was done. Conservation could not be 

 proved from denial of action at a distance. Speaking of the 

 doctrine of transference and transformation of energy, he said 

 it was a convenient working rule, but not true universally. 

 Newton's laws were simple and consistent, but some doubt 

 existed as to how much was definition and how much law or 

 fact. Mr. Swinburne protested against the dilTerence between 

 theory and a working hypothesis being overlooked. AH con- 

 ceptions were based on experience, and ideas of ether and atoms 

 derived from "jelly" and "cricket ball-." We ought also to 

 remember what "explanation" means, viz. describing the un- 

 familiar in terms of the more familiar. It was customary to 

 describe the phenomena of fluids by relerence to solids because 

 we were more familiar with solids ; an intellectual fish would 

 probably do the revtrse. The so-called "Theory of Mag- 

 netism " which breaks up a bar of iron into a number of small 

 pieces, each possessing the properties of the original bar, he 

 regarded as absurd. It was no "explanation" and not a 

 " theory." Ether might be used as a working hypothesis, but 

 must not be treated as an entity. Mr. Blakesley questioned 

 whether transference of energy was always accompanied by 

 transformation, and he did not see why energy should be looked 



upon as (mv) -, in preference to any other subdivision of tbi^ 



factors. As regards effects being proportional to their cause»|, 

 he pointed out that the heating of an electric circuit, and- 

 thermoelectric action, followed laws not linear. Prof. S. Ti 

 Thompson, referring to the demonstration of the law of trans4 

 ference, &c., given on slip 8, said that attempts to translate it f 

 into Latin or Greek at once revealed the ambiguous character of 

 the proof. Speaking of Ohm's law, he pointed out that R, a j 

 constant, was not an essential feature, as Dr. Lodge supposed. I 

 Ohm never said R was constant. In identifying energy, a j 

 difficulty presented itself, for one never came across it as a : 

 single thing but as a product, and in being transformed the j 

 paths of the two factors might possibly be different. Mr. ( 

 Dixon said the whole of geometry and dynamics could bcj 

 based on verbal definitions. The conservation of energy could j 

 be written as : Kinetic energy + potential energy = a constant. 



