other only a few times a second, any shift of the bands would not be capable of detection by the observer. The most satisfactory results could be obtained by using a constant current from a battery of a large number of cells; but as these were not at our command, we attempted to obtain a prolonged discharge from a battery of ten one gallon Leyden jars, a piece of wet string being included in the circuit. The jars were charged by means of the above-mentioned Ruhmkorff coil, suitable arrangements being made for the purpose; and the discharges occasionally succeeded each other so quickly that for some seconds the phenomena were apparently continuous. The duration of each discharge was determined by means of Mr. Boys's wheel of lenses, and was found to exceed second. Not the slightest flicker of the bands could, however, be detected. A check experiment was then performed by dropping a piece of plate glass, which would produce a shift of the bands when placed in the path of the light, from such a height that its effect would last second and to second respectively. In each of these cases a flicker was observed. . From this we conclude that the kathode rays and the positive column, either alone or conjointly, do not affect the velocity of light passing along their path. 8. On the Hysteresis of Iron in an Alternating Magnetic Field. The law connecting hysteresis and induction when the latter reaches a high value has not until now been ascertained. It has hitherto been assumed that the hysteresis would increase continuously with the induction without limit. It is, however, probable that in a slowly performed cycle of change of magnetisation a maximum value of the hysteresis will be reached when the iron is saturated, and that further increase of the number of lines of force induced will produce no further increase in the hysteresis. When a rapidly alternating field is considered the conditions are somewhat different. As the magnetising current is increased the iron reaches its saturation value at an earlier point in each period, thus increasing the rate of change of magnetisation. But it has been shown by different experimenters that the value of the hysteresis per cycle is practically unchanged through wide variations in speed, and hence it may be expected that the hysteresis of iron under all conditions will arrive at a definite maximum. To verify this experimentally, the hysteresis in a small sample of iron was measured, when it was placed between the poles of a powerful electromagnet excited by an alternating current. Both magnet and sample were laminated, the subdivision of the latter being especially fine, in order to eliminate as far as possible errors due to eddy currents. The sheets consisted of soft charcoal-iron of thickness 0085 cm., and between each was a layer of tissue paper. The maximum value of the eddy currents was less than 2 per cent. of the hysteresis. The hysteresis was measured by the rise in temperature of the iron after 90 seconds, the speed of alternation being constant at 103 cycles per second. The sides of the sample were coated with layers of sheet cork, the radiation being very small. At the end sufficient protection could not be allowed owing to the small size of the air-gap, and hence transference of heat was prevented by maintaining equality of temperature between the pole pieces and the sample by means of streams of hot or cold paraffin oil over the pole pieces. All temperatures were measured by thermoelectric couples of german silver and copper. The experiments show that the curve when plotted with the induction as abscissa, and the hysteresis as ordinate, exhibits a flexure at an induction of about 16,000, and becomes practically horizontal at 23,000. This corresponds to a value of intensity of magnetisation of 1,640, which is just the saturation value. The same characteristics are observed when the intensity of magnetisation is taken as the abscissa, the curve bending over until it is almost horizontal at the point of saturation. The experiments prove that the hysteresis of iron is a function, not of induc tion, but of intensity of magnetisation, since both values become constant together, and that the relation between them is not a logarithmic curve, but is a curve showing one flexure, and clearly indicating in its upper portion the condition of the iron represented by Professor Ewing's third stage of magnetisation. WEDNESDAY, SEPTEMBER 18. The following Papers and Report were read:— 1. On the Change of Molecular Refraction in Salts or Acids dissolved in Water. By Dr. J. H. GLADSTONE, F.R.S., and WALTER HIBBERT, F.I.C. The authors had recently undertaken a research on the questions-Does the specific refractive energy of a salt or acid when deduced from its solution in water differ from that of the solid compound? and Does the specific refractive energy vary according to the amount of water? The outcome of the experiments of the authors and others is that the water does bring about in many cases a small alteration, especially in passing from the solid or liquid to the dissolved condition; that this alteration is sometimes an increase, at other times a decrease; and that it depends upon the chemical nature of the compound. Some points of physical interest were, however, noted, and were being more fully examined. One of these is the analogy of this refraction change in several instances with the change in the power to rotate the plane of polarised light as determined by Dr. Perkin. As this small change of refraction evidently indicates some rearrangement of the constituents of the salt or acid in the water, it may throw light upon present theories of solution. The experiments, even those of Kohlrausch and Hallwachs on extremely dilute solutions, do not support the view that the binary compound when greatly diffused tends to exhibit the properties of a gas. There is an evident relation between this change of refraction and the electric conductivity of the solution. Thus, in the acids the order of the two phenomena is the same, the hydrochloric acid showing the greatest effect, rapidly followed by hydrobromic and hydriodic acids; then nitric acid, afterwards sulphuric acid; and at a great distance acetic and other organic acids. In the case of nitric and sulphuric acids the general form of the curves representing the change of electric conductivity and of refraction is similar; in the case of the latter there is a special depression during the rise of the conductivity curve which makes its appearance as a slackening of the rise in the curve representing change of refraction. This connection of the two phenomena is being further carefully examined at present. 2. Report on Electrical Standards.-See Reports, p. 195. 3. On the Choice of Magnetic Units. By Professor SILVANUS P. THOMPSON, F.R.S. Professor Silvanus Thompson pointed out that the giving of names was a detail, and that agreement was wanted upon the units themselves in which magnetic quantities were to be expressed. He agreed with the Standards Committee that the two most important units to be defined were those of magnetic flux and of magnetic potential, and urged that no other units should be defined until these had been tried. But he differed from the suggestion to take the weber as 108 C.G.S. lines as being a unit of too great an order of magnitude to suit practical needs. He preferred simply to take the line, with its natural multiples the kiloline, and the megaline as the unit of flux. If the name weber were given to the line itself the Committee's recommendation would then be identical, so far as this unit is concerned, with that of the American Institute of Electrical Engineers. He agreed with the propositions to adopt the name gauss for the C.G.S. unit of magnetic potential. 4. On some New Methods and Apparatus for the Delineation of Alternate Current Wave Forms. By J. M. BARR, W. B. BURNIE, and CHARLES RODGERS. 5. On Alternating Wave Tracers. By Professor W. E. AYRTON, F.R.S., and T. MATHER. 6. On the Relation between Speed and Voltage in Electric Motors. 7. On some recent Improvements in Measurements of High Temperatures. Illustrated by Apparatus recently acquired by the Kew Observatory Committee. By E. H. GRIFFITHS, F.R.S. SECTION B.-CHEMISTRY. PRESIDENT OF THE SECTION.-Professor R. MELDOLA, F.R.S., FOR.SEC.C.S. THURSDAY, SEPTEMBER 12. The President delivered the following Address:— THE STATE OF CHEMICAL SCIENCE IN 1851. In order to estimate the progress of chemical science since the year 1851, when the British Association last met in this town, it will be of interest for us to endeavour to place ourselves in the position of those who took part in the proceedings of Section B on that occasion. Perhaps the best way of performing this retrograde feat will be to confront the fundamental doctrines of modern chemistry with the state of chemical theory at that period, because at any point in the history of a science the theoretical conceptions in vogue-whether these conceptions have survived to the present time or not-may be taken as the abstract summation of the facts, i.e., of the real and tangible knowledge existing at the period chosen as the standard of reference. Without going too far back in time I may remind you that in 1811 the atomic theory of the chemists was grafted on to the kindred science of physics through the enunciation of the law associated with the name of Avogadro di Quaregna. The rationalising of this law had been accomplished in 1845, but the kinetic theory of gases, which had been foreshadowed by D. Bernoulli in 1738, and in later times by Herapath, Joule, and Krönig, lay buried in the archives of the Royal Society until recently unearthed by Lord Rayleigh and given to the world in 1892 under the authorship of Waterston, the legitimate discoverer. The later developments of this theory did not take place till after the last Ipswich meeting, viz., in 1857-1862, by Clausius, and by Clerk Maxwell in 1860-1867. Thus the kinetic theory of gases of the physicists had not in 1851 acquired the full significance for chemists which it now possesses: the hypothesis of Avogadro was available, analogous conceptions had been advanced by Davy in 1812, and by Ampère in 1814; but no substantial chemical reasons for its adoption were adduced until the year 1846, when Laurent published his work on the law of even numbers of atoes and the nature of the elements in the free state.1 The so-called 'New Chemistry' with which students of the present time are familiar was, in fact, being evolved about the period when the British Association last assembled at Ipswich; but it was not till some years later, and then chiefly through the writings of Laurent and Gerhardt, that the modern views became accepted. It is of interest to note in passing that the nomenclature of organic compounds formed the subject of a report by Dr. Daubeny at that meeting in which he says:-'It has struck me as a matter of surprise that none of the British treatises on Chemistry with which I am acquainted should contain any rules to guide us, either in affixing names to substances newly discovered or 1 Ann. Chim. Phys. [3], 18, 266. in divining the nature and relations of bodies from the appellations attached to them. Nor do I find this deficiency supplied in a manner which to me appears satisfactory when I turn to the writings of Continental chemists.' In a subsequent portion of the report Dr. Daubeny adds:- No name ought, for the sake of convenience, to exceed in length six or seven syllables.' I am afraid the requirements of modern organic chemistry have not enabled us to comply with this condition. Among other physical discoveries which have exerted an important influence on chemical theory the law of Dulong and Petit, indicating the relationship between specific heat and atomic weight, had been announced in 1819, had been subsequently extended to compounds by Neumann, and still later had been placed upon a sure basis by the classical researches of Regnault in 1839. But here, again, it was not till after 1851 that Cannizzaro (1858) gave this law the importance which it now possesses in connection with the determination of atomic weights. Thermo-chemistry as a distinct branch of our science may also be considered to have arisen since 1851, although the foundations were laid before this period by the work of Favre and Silbermann, Andrews, Graham, and especially Hess, whose important generalisation was announced in 1840, and whose claim to just recognition in the history of physical chemistry has been ably advocated in recent times by Ostwald. But the elaboration of thermochemical facts and views in the light of the dynamical theory of heat was first commenced in 1853 by Julius Thomsen, and has since been carried on concurrently with the work of Berthelot in the same field which the latter investigator entered in 1865. Electro-chemistry in 1851 was in an equally rudimentary condition. Davy had published his electro-chemical theory in 1807, and in 1812 Berzelius had put forward those views on electric affinity which became the basis of his dualistic system of formulation. In 1833 Faraday announced his famous law of electro-chemical equivalence, which gave a fatal blow to the conception of Berzelius, and which later (1839-1840) was made use of by Daniell in order to show the untenability of the dualistic system. By 1851 the views of Berzelius had been abandoned, and, so far as chemical theory is concerned, the whole subject may be considered to have been in abeyance at that time. It is of interest to note, however, that in that year Williamson advanced on quite distinct grounds his now well-known theory of atomic interchange between molecules, which theory in a more extended form was developed independently from the physical side and applied to electrolytes by Clausius in 1857. The modern theory of electrolysis associated with the names of Arrhenius, van 't Hoff, and Ostwald is of comparatively recent growth. It appears that Hittorf in 1878 was the first to point out the relationship between electrolytic conductivity and chemical activity, this same author as far back as 1856 having combated the prevailing view that the electric current during electrolysis does the work of overcoming the affinities of the ions. Arrhenius formulated his theory of electrolytic dissociation in 1887, Planck having almost simultaneously arrived at similar views on other grounds. Closely connected with electrolysis is the question of the constitution of solutions, and here again a convergence of work from several distinct fields has led to the creation of a new branch of physical chemistry which may be considered a modern growth. The relationship between the strength of a solution and its freezing point had been discovered by Blagden towards the end of the last century, but in 1851 chemists had no notion that this observation would have any influence on the future development of their science. Another decade elapsed before the law was rediscovered by Rüdorff (1861. and ten vears later was further elaborated by de Coppet. Racult published his nrst work on the freezing point of solutions in 1882, and two years later the relationship between osmotic pressure and the lowering of freezing point was established by II. de Vries, who first approached the subject as a physiologist, through observations on the cell contents of living plants. As the work done in connection with osmotic pressure has had such an important influence on the 'dissociation' theory of solutions, it will be of interest to note that at the last Ipswich meeting Thomas Graham made |