466 



NATURE 



{Sept. 7, 1882 



meant by the velocity of propagation of a wave. In a regular 

 t-ain of waves this was the velocity with wh'ch any given phase 

 of a wave moved forward ; this could easily be observed in the 

 case of waves on water, but in the case of light no wave form 

 could be observed. The velocity determined by Fizeau's method, 

 or by the eclipses of Jupiter's satellites, was not this, but the 

 velocity of propagation of intermissions of light, which if the 

 true velocity of propagation is a function of the wave-length, is 

 not the same as the true velocity ; it is only the same where, as 

 in the case of air, the velocity of propagation is the same for all 

 wave-lengths. Foucault's method (Michelson's) is based on de- 

 termining the angular motion of a mirror between successive 

 reflections, which again is a different quantity from the former 

 two. 



Sir W. Thomson wished to testify that the experiments were 

 made most carefully, and felt unable to suggest any other 

 explanation than Mr. Forbes's, but he felt trong previous objec- 

 tions to accepting it. He pointed out that Mr. Forbes's obser- 

 vations made the vel ocity of propagation smaller for waves of 

 shorter period, whilst from the analogy of sound in elastic bodies 

 we should expect the opposite. 



SECTION B— Chemical Science 

 On the Reversals of the Spectral Lines of Metals. By Profes- 

 sors Liveing, M.A., F.R.S., and J. Dewar, M.A., F.R.S.— The 

 authors have a twofold object in view in the study of this subject, 

 (1) to trace the parallel between the condition of the elements as 

 they exist in the sun and those in which they may be placed on 

 the earth ; (2), that a knowledge of the reversible lines might 

 aid to distinguish those due directly to the vibrations of the 

 molecules and those produced by superposition of waves or by 

 some strain upon the molecules, such as the electric arc might 

 produce. They classify the reversals, as follows ; (1) Reversals 

 produced when the expanded line itself forms the background 

 against which the absorption line is narrowed because the den- 

 sity is less than that of the emitted vapours. Thseare the one; 

 most generally known. (2) Reversals in which there is little or 

 no expansion of the lines, the background being either the hot 

 walls and end of the tube, the hot pole of the arc, or such part 

 of the spectrum which is so full of lines as to be nearly continuous. 

 Photographs exhibiting the reversals of the lines of iron and 

 other metal-, were shown. (3) Reversals in which the back- 

 ground U produced by the expansion of a line of some other 

 metal. Photographs were shown in which the lines of iron and 

 other metals were seen reversed on the expanded lines of mag- 

 nesium. (4) Reversals produced by the introduction into the 

 crucible in which the arc was of a gentle current of hydrogen, 

 coal gas or ammonia, by which means the metallic lines were 

 almost swept away and the continuous spectrum increased. (5) 

 When a carbon tube passed through a perforation in a block of 

 lime is made the positive electrode of the arc, and a carbon rod 

 passed into another perforation so as to meet the tube in the 

 centre of the block, be made the negative electrode, the tube 

 becomes gradually heated up, and in the direct line of the tube 

 the lines are seen bright, because there is no background, but are 

 seen reversed Jagainst the hot walls of the tube. Further the 

 effects of the gradual increasing temperature were traced, as the 

 tube was gradually heated. (6) A double reversal of lines is 

 occasionally observed, and an instance was shown, in which the 

 expansion of the magnesium lines between K and H, bad taken 

 place to such an extent as to produce the reversal of the most 

 refrangible of the cyanogen bands ; the magnesium producing a 

 broad absorption band again -t which the magnesium triplet stood 

 out bright and sharp. It is probable that this arises from the less 

 dense but intensely heated magnesium vapour being pushed for- 

 ward up the tube by the sudden burst of vapour produced when 

 a fre-h piece of metal is dropped into the arc. 



On the Legal Flashing Tat for Petroleum, by F. A. Abel, C.B., 

 F.R.S. — The defects of the old legal flashing test, called the 

 open test, and the test used in the United States, known as the 

 fire te-t, led to the introduction of the close-flasbin<* te-t, which 

 was legalised by Act of Parliament in 1S79. Theauthorexhibitcd 

 the apparatus required, and described the method of Using this 

 test. This test has since been adopted in Germany and the 

 United States, and the investigations conducted in the former 

 country by Dr. Foerster and others, showed what had already 

 been observed by the author, that the results obtained with the 

 apparatus were influenced by atmospheric pressure. The most 



recent investigations of the author and Mr. B. Redwood, have 

 shovn that a variation in the height of the barometer of oieinch, 

 was sufficient to produce a change of two degrees Fahrenheit in 

 the flashing point of one and the same sample of oil. Further, 

 it appears that the changes of atmospheric temperature have 

 some influence on the flashing point of a sample of oil, and not 

 only is it necessary to c >ol down the sample of oil immediately 

 before testing if, when its temperature exceeds 65° F., but it is 

 imperative, in cases where the oil has been stored in localities, 

 the temperature of which is above 65° F., to maintain the oil at 

 a low temperature for a considerable peri od before testing it. 

 In consequence of this effect of changes of atmospheric tempe- 

 rature, some difficulties have arisen in applying this test in 

 India, and investigations are at present being conducted, the 

 object of which is t > a-certain the conditions required for securing 

 the attainment of tru-tworthy results by the application of this 

 test in tropical climates. 



On the Boiling Points and Vapour Tensions of Mercury, of 

 Sulphur, and of some Compounds of Carbon, determined by means 

 of the Hydrogen Thermometer, by Professor J. M. Crafts. — A 

 description was given of the hydrogen thermometer used, the 

 replacement of air by hydrogen was adopted because of the 

 more rapid flow of hydrogen through a capillary tube, further, 

 the bulb of the thermometer could be reduced from 200-500 cc. 

 to i-iocc. The thermometer was one of constant volume in 

 which an electric contact between the mercury in the manometer 

 and a platinum point causes a current to excite a magnet and 

 clo«e a cock to arrest the flow of mercury into the manometer 

 tube at the moment the gas attains a. fixed volume, as determined 

 by the surface of the mercury touching the platinum point. The 

 boiling point of mercury has been redetermined, an 1 found to be 

 357° (at the normal pressure), that of sulphur was found to be 

 one degree lower than that assigned to it by Regnault. Naph- 

 thalene b. p. 2iS'o8 (bar. 763 mm.), and loenzophenone, b. p. 

 306"' I C. (bar. 760 mm.), were also used to obtain constant 

 temperatures near 200° and 300°. The boiling points of these 

 two substances were determined under reduced pressures varying 

 from 87 to 2,300 mm., giving a series of temperatures that can 

 be easily established and maintained for any length of time, and 

 ranging from 140° to 350°. It is probable that benzene may 

 be easily obtained sufficiently pure to be used in a similar 

 manner. A series of determinations of the boiling points of 

 several carbon compounds have been made, from which it appears 

 that successive, similar additions to the molecular weight do not 

 cause the boiling points to rise by a constant quantity as supposed 

 by Kopp, but that in a large number of cases the increments to 

 the boiling temperatures diminish by a constant quantity. 



The Velocity of Explosion of a Mixture of Carbonic Oxide and 

 Oxygen, with varying quantities of Aqueous Vapour, By II. B. 

 Dixon, M.A. — The author has compared the velocities of ex- 

 plosion of mixtures of carbonic oxide and oxygen with varying 

 quantities of aqueous vapour, by observing the pressure registered 

 in a mercurial gauge attached to the endiometer in which the 

 gases were fired. In each experiment the same mass of carbonic 

 oxide and oxygen was exploded at nearly constant volume and 

 temperature. The gauge was U shaped and contained air in the 

 closed limb. An index similar to that used in Six's thermometer 

 was carried up and left at the highest point reached by the 

 mercury. Near the bend of the guage two bulbs were blown to 

 act as reservoirs, enabling the mercury to be lowered in the 

 endiometer, without allowing air to escape from the closed limb. 

 The endiometer was dried at So" by drawing through it, for half 

 an hour, air which had pas c ed through tubes containing sulphuric 

 acid, and a tube containing phosphoric pentoxide. It was found 

 that in this way just sufficient aqueous vapour remained in the 

 tube to enable the explosion to take place slowly when the 

 sparks from a RbumkorrT coil was passed through the mixed 

 gases. In the first experiments several sparks were passed before 

 the erases took fire. Experiments were made in which measured 

 quantities of aqueous vapour were added, and the vapour kept 

 hel j w saturation, and also with the gases saturated with moisture. 

 The results obtained in these experiments show the pressure 

 registered to increase with the amount of moisture present in the 

 gases, and to be the greatest when the gases are saturated. 



On the Activity of Oxygen, and the mode of formation of 

 Hydrogen Dioxi'te, by C. T. Kingzett, F.I.C., F.C.S.— An 

 account is given of the various view; held regarding the forma- 

 tion of ozone and hydrogen peroxide by slow oxidation, in the 

 formation of the latter by the slow oxidation of the terpenes 

 the author considers that an organic peroxide is first iormed, 



