Jan. 6, 1887] 



NATURE 



shot (as imagined by tlie late Prof. Marreco and Mr. D. P. 

 Morrison), or by a fall of roof, a train of mine waggons that has 

 just passed, or any other accidental circumstance, and subse- 

 quently carried past the mouth of the shot-hole at the instant 

 the flame issues from it." 



Immediately after the passage quoted above the Commissioners 

 proceed to say : — 



" The following facts relating to the part played by dust in 

 coal-mine explosions may, however, now be regarded as cou- 

 clusis'ely established : — 



" I. The occurrence of a blown-out shot in working-places 

 where very highly iii/lamiiialile coal-dust exists in grej-t abund- 

 ance, may, even in the total absence of fire-damp, possibly give 

 rise to violent explosions, or may at any rate be followed by the 

 propagation of flame through very considerable areas, and even 

 by the communication of flame to distant parts of the workings 

 where explosive gas-mixtures, or dust-deposits in association 

 with non-explosive gas-mixtures, exist." 



'* 2. The occurrence of a blown-out shot in localities lohere 

 only small proportions of fire-damp exist in the air in the pre- 

 sence of 'even comparatively slightly injlainvta^de or actually 

 non-inflammable, but very fine, dry, ani porous dusts may 

 give rise to explosions the flame from which may reach to 

 distant localities, where either gas accumulations or deposits of 

 inflammable coal-dust may be inflamed, and may extend the 

 disastrous results to other regions." 



This has the appearance of conceding all that is asked, but 

 when read in the light of the first quotation it leaves the matter 

 in considerable doubt. Indeed, it was stated at the inquest on 

 Altofts explosion that the proprietors of that colliery had not 

 gathered from the Commissioners' Report that ihey were running 

 any risk of an explosion, such as the one that happened ; and 

 at the inquest on Elemore explosion, which has been ad- 

 journed until the tSth iujt., Mr. Lishman, the manager, gave 

 utterance to similar sentiments. Be this as it may, it is obvious 

 that legislative measures ought to be adopted without further 

 delay, with the object of rendering the recurrence of coal-dust 

 explosions impossible for the future. In providing against them 

 it must also Le recollected that a local explosion of fire-damp, 

 such as the one which originated Mardy explosion, produces 

 exactly the same result as a blown-out shot fired under the most 

 favourable conditions imaginable. 



Cardifli', January 5 W. Calloway 



The Cambridge Cholera Fungus 



In your issue of December 23 (p. 171) appears a letter from 

 Dr. E. Klein, in which that gentleman attempts to show that 

 the micro-organisms found by Dr. Graham Brown, Mr. Sher- 

 rington, and myself in the substance of the mucous membrane of 

 the small intestine in cases of Cholera asiatica are nothing more 

 than "common mould (probably aspergillus)," which has 

 grown on and into the tissue during the process of hardening. 

 We were and are, however, perfectly well acquainted with the 

 fact that imperfectly preserved animal tissues are liable to be 

 invaded by various forms of fungi, and took, therefore, precau- 

 tions which we believe to be ample to prevent such contamina- 

 tion of our material. Moreover, the presence of the micro- 

 organisms in certain parts of the tissues only, their absence in 

 others or on the surface of the specimens, the fact that their 

 presence in the part is accompanied by anatomical changes 

 which could not have taken place during the process of harden- 

 ing, and, most of all, the characters of the micro-organisms 

 themselves, render such an hypothesis as that brought forward by 

 Dr. Klein absolutely unacceptable. 



It is unnecessary for me to answer all the arguments ad- 

 vanced by Dr. Klein in support of his views on this subject. 

 They prove nothing more than that fungi grow on and in animal 

 tissues which are not adequately preserved — a fact which no one 

 will doubt. That, on the other hand, the micro-organisms found 

 by us are of this nature is a matter which neither Dr. Klein nor 

 any other person who is unacquainted with the facts is in a 

 position to decide. Since a short preliminai-y account only of 

 the work done by Dr. Graham Brown, Mr. Sherrington, and 

 myself, on the pathology of cholera has as yet been published. 

 Dr. Klein has not before him the facts on which alone a decision 

 of any value is possible. Charles Roy 



Pathological Laboratory, New Museums, Cambridge 

 December 30, 1886 



An Error in Maxvvrell's "Electricity and Magnetism" 



The criticism of Mr. McConnel upon Maxwell's derivation 

 of the inductive action of currents from the principle of energy 

 is perfectly correct. It is inconsistent with the experimental 

 facts appealed to by Mr. McConnel and Mr. Maxwell's own 

 treatment of the field as the seat of electro- kinetic energy. 



In the excellent treatise of Messrs. M.ascart and Joubert, a 

 similar misleading appeal is made to Helmholtz's proof, and I 

 have little doubt that Maxwell has correctly stated it. I should 

 be inclined to think that the existence of the energy of the field 

 was not distinctly present to Helmholtz's mind. 



Maxwell, as is well known, by an ingenious application of 

 Lagrange's equations of motion, proves that, in the case of two 

 currents, this electro-kinetic energy y, is given by the equation — 



T, ^\{L^i{- -V Mi^ii + LJ.?), 

 ■ -cos e 

 where M = I \ dsds' taken round both circuits, and Z, 



and L.2 are similar expressions for the separate circuits. 



I believe, though I dare not trespass upon your space to give 

 the reasoning in extenso, that this result may be obtained some- 

 what more simply and without the use of the Lagrangean equa- 

 tions, a treatment which has the disadvantage of assuming the 

 electric co-ordinates y^ and/^. the currents being j/, and r.^. Then 

 the equation of energy becomes 



dT' dT,„ 



.■4,i, + A^i., = — + -t- ^1/,- + H^^, 



dt dt 



dT.n dM 



where T",,, is material kinetic energy, and — ■ - i-f., 



dt ' dt 



supposing the circuits rigid. Therefore 

 A^iy -F AJ,_ 



f 



-<J.J., + Mi^) +JiJ.\, 



^tA-{L,i, + Mi.:^ + Ji,iA - 



{dt ) ( dt 



reducing to Mr. McConnel's equation, when the currents are 

 constant. 



In the case of two circuits thus moving in connection with 

 their batteries we may infer that A-^ and A.^ must be such func- 

 tions of ii and 4, and the coefficients of configuration, that, when 

 the suffixes are interchanged in the expression for A^, that for yi.j 

 must result, and vice versA. If this be so, then the aforesaid 

 equation necessitates the separate equations — 

 d 

 A, ^ - (L,i, + .)//,) + A\i, ; 

 dt 

 d 

 A,. = -{LJ.,-I- Mi,) -f A'.,;.,. 

 dt 

 Or Maxwell's equations are obtained without the use of 

 Lagrange. Henry \V. Watson 



Berkeswell Rectory, near Coventry 



The Manipulation of Glass containing Lead 

 In a note on this subject in Nature (Dec. 16, p. 150), Mr. 

 H. G. Madan has made a suggestion which is likely to be very 

 valuable to those who require to manipulate "combustion- 

 tubing " before the blow-pipe. But, in proposing the employ- 

 ment of oxygen in place of air to produce flames for heating 

 glass containing lead, Mr. Madan introduces a refinement which 

 is unnecessary ; for lead-glass may be quite as easily manipu- 

 lated in flames produced by plain air and gas as soda-glass 

 itself The pointed flame should be employed for small objects, 

 and the oxidising brush-flame in the case of larger objects. By 

 the oxidising brush-flame, however, I do not mean the brush- 

 flame as ordinarily employed, but one to which the air is supplied 

 liberally through an air-tube without any contraction at its end, 

 and at a steady pressure from a good blower ; care being taken, 

 on the other hand, not to introduce such an excess of air as to 

 reduce the temperature of the flame. 



In his note, Mr. Madan quotes me assaying, in the " Methods 

 of Glass-blowing," that the reducti m of lead-glass may be 

 prevented or remedied by holding the glass a little in front of 

 the visible flame, with the comment that there is hardly enough 

 heat in that region to do all that is required in the manipulation 



