December 14, 191 1] 



NATURE 



235 



counted on a zinc sulphide screen at a mean rate of /a per 

 second, then the probabiHty of occurrence of a time 

 interval, of length between t and t + 5f, is /xc -'*^. This 

 formula may be applied to test whether two a particles are 

 given ofl simultaneously from a disintegrating atom or 

 whether in any source of o particles there exist two 

 successive o-ray products, the latter being of short life. 

 In the previous paper uranium and polonium were shown 

 not to give such irregularities, and in the present paper 

 the same result has been found for actinium and thorium 

 active deposits, although experiments of various investi- 

 gators pointed to the probability of positive results. The 

 experiments further suggest a lateral disintegration in 

 thorium active deposit, and this is proved to be the case 

 bv results, which show that the two a-ray products in 

 'J'hor. Act. Dep. (Th. C, and C,) do not give an equal 

 number of o particles when the active deposit is in equi- 

 librium which is required by the ordinary disintegration 

 theory. Thus it . is concluded that of the atoms Th. C, 

 35 per cent, give rise to o particles of 48 cm. range and 

 f)5 per cent, to a particles of 8-5 cm. range, with probably 

 the intermediate emission of )8 particles. Various cognate 

 questions are also discussed in the paper. — S. W. J. Smith, 

 W. White, and S. G. Barker : The magnetic transition 

 temperature of cementite. The temperature at_ which 

 cementite (carbide of iron) loses its ferromagnetism is deter- 

 mined sufficiently accurately for purposes of thermo 

 magnetic analysis, and examples are given to show the 

 possibility of using the thermomagnetic properties of 

 cementite to determine whether that substance is present 

 in any iron-carbon alloy. 



Manchester. 

 Literart' and Philosophical Society. November 28. — 

 Prof. F. E. Weiss in the chair.— Dr. J. N. Pring: and 

 D. M. Fairiie : The synthesis of hydrocarbons and their 

 stability at high temperatures and pressures. The reaction 

 between carbon and hydrogen, which has been found to 

 produce methane at all temperatures up to 1600°, has been 

 examined at various pressures up to 200 atmospheres. In 

 this way it has been possible to evaluate and verify the 

 equilibrium in the formation of methane, arising accord- 

 ing to the equation C-|-2Hj:Z^CH,. In accordance with 

 this reaction it follows from the law of mass action that 



" — ^,= K, a constant at any given temperature. This was 



found to be the case in these experiments when any par- 

 ticular form of carbon was used. The yield of methane 

 was found to increase with the pressure to the extent 

 demanded by the above formula. At atmospheric pressure 

 the equilibrium value with graphite corresponds to 024 per 

 cent, at 1200° and 006 per cent, at 1575 . Values which 

 were considerably higher were obtained with amorphous 

 carbon, viz. an equilibrium which corresponds to 038 per 

 cent, at 1200° and o-i8 per cent, at 1550°. This divergence 

 is due to the fact that amorphous carbon is unstable at 

 these temperatures, and gives temporarily " false " or 

 " metastable " equilibria, which are higher than the true 

 values. The great inertness of methane to decomposition 

 enables this false equilibrium value to persist for some 

 time. The velocity of the reaction between carbon and 

 hydrogen is very much increased at high pressures. No 

 other saturated hydrocarbon is formed or can exist at 

 temperatures above 1100°, and at pressures up to 200 

 atmospheres. The heat evolved in the transformation of 

 carbon into graphite can be calculated from the data 

 obtained in this work by moans of certain deductions of 

 van 't HofT. The rfsults show that this heat of trans- 

 formation increases in tin- range of temperature between 

 1100° and 1600°. It follows from this, in accordance with 

 the law of KirchhofT, that the specific heat of carbon 

 increases more rapidly and is higher than that of graphite 

 at these temperatures, whereas the reverse would follow 

 from the accepted values of Kuntz and of Weber, which 

 ! do not therefore apply at high temperatures. 



Dublin. 

 Royal •" ublin f»oci tv. Novetiber 28. — Prof. T.Johnson 

 n the chair. — Sir Howard Qrubb : Improvements in 

 iiatorial telescope mountings. The paper is divided into 

 'I parts, one dealing with the anti-friction arrangements 

 the large equatorials which are at present in course of 



NO. 2198, VOL. 88] 



construction for Johannesburg, Santiago de Chile, and 

 Madrid. This first portion of the paper describes the 

 newly designed apparatus, and reports upon the result of 

 the first trials. The apparatus described is a development 

 of that used in Sir Howard Grubb's large instruments, 

 improved in many ways and adapted for use with the 

 modern ball or cylinder bearings, which have been found 

 to give very satisfactory results. The second portion of 

 the paper deals with a new arrangement for a differential 

 hour circle. There are two designs described, one of which 

 has been suggested by Sir David Gill, and is being adapted 

 to the Johannesburg and Santiago telescopes. In this 

 arrangement the differential hour circle is kept continually 

 moving by a series of electric contacts from the sidereal 

 clock of the observatory. The other form which has been 

 designed by the author of the paper has been adapted to 

 the Madrid equatorial, and in this case the differential 

 hour circle is kept moving backwards as respects the polar 

 axis by a small piece of clockwork carried on the axis 

 itself, and this enables actual right ascensions to be read 

 off by this circle from a fixed vernier. — Prof. T. Johnson : 

 Forbesia cancellata, gen. et sp. nov. This fossil plant was 

 collected by the Geological Survey of Ireland in 185 1 from 

 the Lower Carboniferous of co. Cork, and named in 1864 

 by W. H. Baily " Sphenopteris, sp." The fossil shows 

 marked dichotomy in all its parts, even in the ultimate 

 pinnule segmentation. There is no sign of vascular tissue, 

 but axis and frond are alike honeycombed. The chambers 

 are lined with rows of parenchymatous cells and their 

 septa, apparently strengthened by sclerotic bands connected 

 with submarginal vertical striae. One specimen shows 

 signs of a fruiting condition comparable with that in 

 Cephalopteris, Nathorst, from the Upper Devonian of Bear 

 Island. On the assumption that Forbesia is evascular, the 

 author considers it to be the most primitive of the primo- 

 filices yet found. Comparison with Sphenopteris devonica, 

 Unger and Richter, is made. 



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