4o6 



NA TURE 



[August 23, 1894 



that the balance of assimilation and nutrition, upon the proper 

 maintenance of which the health of the whole organism imme- 

 diately depends, hinges upon the integrity of such obscure 

 structures ; and it is the maintenance of this balance which con- 

 stitutes health, its disturbance, disease. Nor, on the other 

 hand, dare we, as the investigation of the attraction-particle 

 has shown, afford to disregard the most minute detail of struc- 

 ture of the body. 



■ . *' AU is c^ncentcr'd in A life intense, 



Where not a beam, nor .lir, nor leaf is lost. 

 But hath a part of being." 



PHYSICS AT THE BRITISH ASSOCIATIO.Y. 



\ FTER the President's address on Thursday morning. Lord 

 ■'*■ Kelvin opened the proceedings in Section .\ with an 

 account of some preliminary experiments made by himself and 

 Mr. Maclean on the electrification of air by the subtraction of 

 water from it. The subject is one in which Lord Kelvin has 

 been for many years interested, and he commenced experiment- 

 ing on it as far back as 1868. The nature of the results now 

 obtained was illustrated by his insisting that the proper title of 

 the paper was " Preliminary experiments lo finJ if subtraction 

 of water from air electrifies it" (and not as in the /smj wa/— 

 " Experiments /ri7:7«^ the electrification of air "). In the pre- 

 sent investigation a large U-tube was used. One branch of this 

 was filled with pumice-stone soaked in sulphuric acid ; the other 

 was simply varnished inside and out. By means of a platinum 

 wire touching the pumice, connection was made with a quadrant 

 electrometer. A metal cylinder screened the tube from external 

 influence. Air from an ordinary blow-pipe bellows was blown 

 through the tube steadily for an hour; and the electrometer 

 showed an electrification rising gradually to about nine volts 

 positive. This shows that the passage of the air through the 

 tube gave positive electricity to the acid, and therefore sent 

 away the dried air electrified negatively. No such effect was 

 observed when the pumice was moistened with water instead 

 of sulphuric acid. The experiments are to be repeated with 

 precautions to prevent any babbling of the air through liquid 

 in the tube ; for it was observed that the strong positive electri- 

 fication of the tube (when acid or calcium chloride was used) 

 seemed to commence suddenly .is soon as a gurgling sound, 

 due to bubbling through free liquid, began to be heard. 

 The authors have rever>cd the conditions, and have first dried air 

 by passing it over sulphuric pumice, and then passed it through 

 a tube containing moistened pumice. The tube became 

 negatively electrified, but this may have been due to the 

 negative electrification of the dry entering air. This experi- 

 ment is to be repeated with dried and dis-electrified air. 

 Lord Kelvin also described certain preliminary experiments 

 made by himself and .Mr. Gait with the object of comparing the 

 discharge of a Leyden jar through dilTcrent branches of a 

 divided channel. The metallic part of the discharge channel 

 was divided between two wires of conducting metal, each con- 

 sisting in part of a test-wire. Each of the two test-wires con- 

 sisted of 51 cm. of platinum wire of 0006 cm. diameter and 

 12 ohms resistance stretched in a glass tube. One end was 

 fixed to a solid brass mounting, and the other w.as alt.iched to a 

 fine -spring carrying a light arm for multiplying the motion. 

 The testing elTect was the heat developed in the test-wire by 

 the discharge, as shown by the elongation, the amount of which 

 was measured by a tracing on sooted paper carried by a drum. 

 Tte wires lo be tested were generally of the same length. 

 When they were of the same material but of dilTercnl diameters, 

 the leiling elongation showed, as might be expected, that the 

 tesi-wire in the branch onlalning the thicker wire was more 

 heaed than the other. With wires of various nonmagnetic 

 materials, of the same resi-tanccs but different lengths and 

 diame'eri, Ihc testing elongations were very nearly equal. In 

 one experiment two equal copper wires were used, but one 

 of them was coiled into a helix ; the testing elongation in this 

 branch wa* less than half of that in the straight branch. Lastly 

 an iron wire wxs compared wiih a platinoid wire of equal resist- 

 ance but greater diameter. The healing cficct in the platinoid 

 branch was nearly one-and-a-half times as great as in the iron 

 branch. This is interesting in relation to Lodge's experiments 

 on alirrnaiive paths, which were not decisive in showing any 

 C' •iirily of copperovcr iron of the same steady ohmic 



'' •■ even showed a .seeming superiority of the iron 



lo; ^.....-.i, , in the discharge of a Leyden jar. 



NO. 1295, VOL. 50] 



Prof. Oliver Lodge followed with a communication on 

 "photo-electric leakage." It is known that a negative charge 

 on an electrified surface escapes much more rapidly when the 

 surface is illuminated with ultraviolet light (Halhvach's experi- 

 ment). Prof. Lodge has investigated the rate of discharge for a 

 number of substances under positive as well as negative electrifi- 

 cation, and in hydrogen as well as air. He finds that when the 

 inside of an electrified pewter-pot is illuminated, it does not 

 leak ; but when the edge is illuminated, it leaks rapidly. Thus 

 the leak.age appears to be a matter of surface-tension, and not of 

 potential. In the discussion which followed. Prof S. P. 

 Thompson stated that he had verified the statement made by 

 Elster and Geitl.ihat when the light is polarised the effect depends 

 upon the pkane of polarisation, the leakage being most rapid 

 when the Fresnellian vibrations are in such a direction as to 

 " chop into " the surface. He has found an analogous difference 

 in the action on selenium cells. 



Mr. G. H. Bryan presented the second part of his report on 

 the present state of knowledge in thermodynamics. In a 

 lengthy and valuable paper he discusses the limitations to the 

 law of distribution of energy in the kinetic theory. He deals 

 primarily with the so called Boltzmann-Maxwell law of distri- 

 bution of energy among the molecules of a gas, which law forms 

 the basis of the kinetic theory of gases. One of the main 

 points kept in view has been to show, as far as possible, where 

 to draw the line between dynamical systems which do, and 

 dynamical systems which do not satisfy the law in question. 

 A great advance in the subject is due to the extension of the 

 use of generalised co-ordinates, by which greater generality has 

 been given to results, and the analysis has been much simpli- 

 fied, as a comparison of Bollzmann's early papers with modern 

 writings abundantly lestifie-'. .V further simplificatijn h,as been 

 effected by the extensive use of the Jacobian notation in this 

 report. The report is divided into three sections. In Section I. 

 the l.iw is regarded in the aspect of a general dynamical 

 theorem without reference to any particular applications, and 

 without taking into account the elTect of collision^. Section II. 

 treats of its application to a system of bodies colliding with one 

 another indiscriminately, and partaking of the nature of gas 

 molecules. .Section III. deals briefly with certain researches 

 relating to the connection between the Boltzmann-Maxwell law 

 and the Theory of Probability, the Virial Equation, and the 

 Second Law of Thermodynamics. With regard to non-collid- 

 ing systems (Section I.), it may be asserted that a large portion 

 of our progress has been made in, firstly, showing that Max- 

 well's demonstrations are faulty and unsatisf.ictory, and by 

 subsequently discovering fresh methods of proof, which, while 

 leading to the same general conclusions, show more clearly the 

 limitations and c inditions under which these conclusions hold 

 good. Test cases of Maxwell's law are given, and also an 

 account of Mr. Culverwell's criticism of the " decisive " test case 

 by which Loid Kelvin claims lo have effectually disposed of the 

 law. Ic is urged th.at uniformity of nomenclature is most desir- 

 able in this as in other branches of science, and hence that 

 some definite understanding should be agreed on as lo what 

 precisely constitutes the Boltzmann-Maxwell law. The follow- 

 ing statements are recommended :— (l) That the distribution of 

 a large number of molecules or other dynamical systems of the 

 same or different kinds in which the coordinates (</) and mo- 

 menta (/) of each system are so arranged that the number of 

 systems in the neighbourhood of any given slate is propor- 

 tional to 



<:-*■=,//, d/>„,l^i <ll„, 



It being the same for all the kinds of molecules or systems, be 

 called the Bollzmann-Maxwcll distribulion. (2) That the l.iw 

 which asserts the permanence of the Bohzmaiin-Maxwell dis- 

 tribution in any particular case be called the liollzmann-Max- 

 well law. { 3) That in future these names be not applied to 

 any corollaries such as that which asserts the equality of the 

 average value of the squares into which the kinetic energy can 

 be split up. That corollary may be called Maxwell's law of 

 partition of kinetic energy. 



The proof of the Boltzmann-Maxwell law, ami the as- 

 sumptions involved in it, may now be regarded .as fully satis- 

 factory for gases whose molecules collide with one another to a 

 certain extent at random, but in a medium in which tiie mole- 

 cules can never escape from one another's inlljencc the subject 

 still presents very grave difficulties. 



On Friday the Section held a joint meeting with Section G, 

 at the headquarters of the latter in Kcble Hall. The first sub- 



