262 



NA TURE 



[January 13, 1898 



lengths 3, 6, 9, 12, 15 and 18 centimetres corresponding to 

 dimension ratios 16, 32, 48, 64, 80 and 96. 



Curves (2) and (3) represent similar changes in different steel 

 wires, where the dimension ratio was varied by altering the 

 diameter of the wire and keeping the length constant. 



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An almost identical curve to No. i is obtained by plotting 

 against the dimension ratio the percentage permanent magnetic 

 loss each piece suffers due to the process of alternate heatings 

 and coolings ; and as this is, without doubt, dependent on the 

 self-demagnetising force in the magnet, it is evident the co- 

 efficient is also a function of the demagnetising force, and is 

 principally varied by this, at least for a given range of dimension 

 ratios. 



The ultimate cause determining the abnormal negative co- 

 efficient in steel music wires of large dimension ratios is not yet 

 completely made out, but experiments now in progress seem to 

 indicate that it is the effect of the drawing in the process of 

 manufacture. 



" A Note on some further Determinations of the Dielectric 

 •Constants of Organic Bodies and Electrolytes at very Low Tem- 

 peratures." By Prof. James Dewar, F.R.S., and Prof. J. A. 

 Fleming, F. R.S. 



December J 6, 1897.— " Memoir on the Integration of Partial 

 Differential Equations of the Second Order in Three Independent 

 Variables, when an Intermediary Integral does not exist in 

 general." By A. R. Forsyth, F.R.S , Sadlerian Professor in 

 the University of Cambridge. 



The memoir discusses the theory of partial differential equa- 

 tions of the second order in one dependent and three independent 

 variables ; and the method adopted is seen, without difficulty, to 

 be applicable to equations which involve more than three inde- 

 pendent variables and which can be of order higher than the 

 second. 



In order to solve a given equation, a system of subsidiary 

 equations is constructed ; and the system is made up of two 

 parts. One of these parts is a set of simultaneous partial 

 differential equations in two independent variables and a number 

 of dependent variables, this number being one more than the 

 number of the equations. An integral equivalent of this part 

 accordingly contains an undetermined quantity. The other of 

 the parts is a set of equations in a single independent variable ; 

 it appears that the set of equations in the second part can be 

 consistently satisfied by a determination of the unknown 

 quantity emerging from the first part. 



The first of the three sections, into which the paper is divided, 

 deals with the general theory, and indicates a method whereby 

 subsidiary equations for an equation F = o of any degree in the 

 derivatives of the second order can be constructed. If integrable 

 combinations of the subsidiary system are not obtainable, an 

 extension of the method shows how equations of higher order 

 (when obtainable) can be deduced and associated with the given 

 equation. 



The second of the three sections deals with those equations of 

 which the characteristic invariant is resolvable ; and some 

 examples are given, alike of equations for which the integration 



NO. 1472, VOL. 57] 



of the initial subsidiary .system is possible, and of equations for 



which the extended method must be used. 



The third of the three sections deals with those equations of 



which the characteristic invariant is irresolvable. Of such 



equations the most interesting examples are the potential 

 equation and other equations in 

 mathematical physics ; and the 

 theory is applied to some of these 

 equations in detail, leading to some 

 new solutions. 



" On the Occlusion of Hydrogen 

 and Oxygen by Palladium." By 

 Ludwig Mond, Ph.D., F.R.S., 

 William Ramsay, Ph.D., F.R.S., 

 and John Shields, D Sc, Ph.D. 



Palladium black prepared in the 

 same way as platinum black con- 

 tains I '65 per cent, of oxygen, 

 which cannot be removed in vacuo 

 at a dull red heat. On heating in 

 an atmosphere of oxygen the 

 amount absorbed up to a red heat 

 was about one and a half times as 

 much as corresponds with the 

 formula PdoO, and this also could 

 not be extracted at a dull red heat 

 in vacuo. 



A comparative study of the oc- 

 clusion of hydrogen by palladium 

 black, sponge and foil was made; and, after taking into 

 consideration .some observations made by Graham and Dewar, 

 it was found that no matter whether the palladium exists as 

 black, sponge, foil, wire, or compact metal, or whether it is 

 charged by direct exposure to hydrogen gas (the proper con- 

 ditions being observed, as explained), or charged electrolytically, 

 the amount of hydrogen occluded in each case is approximately 

 the same, the atomic ratio palladium : hydrogen varying be- 

 tween I '37 and i '47. 



The bulk of the hydrogen occluded by palladium black and 

 sponge can be pumped off again at the ordinary temperature in 

 vacuo. 



The heats evolved per gram of hydrogen and oxygen occluded 

 by palladium black are + 46*4 K (4640 ^cal) and -f ii-2K 

 (ii20^-cal) respectively, the latter value being in harmony with 

 the view that the absorption of oxygen is a true phenomenon 

 of oxidation. 



With respect to the supposed formation of a definite chemical 

 compound on the occlusion of hydrogen, it is shown that Troost 

 and Hautefeuille's deduction that Pd.jH is formed is not 

 warranted. If any hydride is produced at all, it probably con- 

 tains at least as much hydrogen as that required by the formula 

 PdsHj first suggested by Dewar. 



It is also shown that the heats of occlusion of hydrogen in 

 platinum and palladium black are not in favour of the view which 

 has sometimes been put forward, that the heat of occlusion of 

 a gas represents the heat of condensation or liquefaction of the 

 gas in the capillary pores of the absorbing substance. 



Linnean Society, December 16, 1897. — Prank Crisp, Trea- 

 surer and Vice-President, in the chair. — Mr. W. Carruthers, 

 F. R.S., exhibited and made remarks upon a fungus, Kossetlinia 

 ligniaria, which had been found to attack living ash trees, 

 eventually causing the death of the tree. Additional observa- 

 tions were made by Mr. George Murray and Prof. Farmer. — ■ 

 Mr. Edward Step exhibited two specimens of a Hermit Crab, 

 Eupagurus Prideauxi, from Portscatho, Cornwall. Both were 

 found naked and in rock-cavities, and special interest attached 

 to the fact that, in the absence of the well-known molluscan 

 shell which the species affects, ,each specimen was incrusted at 

 precisely the same regions of its exterior by " acorn-shells."— 

 The Rev. T. R. Stebbing gave an account of the habits of this 

 and other species of the genus Eupagurus, directing special at- 

 tention to the work of Aurivillius ; and Prof Howes remarked 

 that it was on record that in the absence of a shell the bowl of 

 a clay-pipe did not come amiss to these animals, and that they 

 will readily utilise broken test-tubes. — ^Mr. H. M. Bernard read 

 a paper on the affinities of the Madreporarian genus Alveopora. 

 The question discussed was one of much interest, owing to the 

 claim advanced by Dana, that Alveopora is a survival of the 

 great Palceozoic family Favositicicv. This claim was rejected by 



