October 19, 1893] 



NATURE 



fo= 



last edition of a text-book or compendium and tracing the steps 

 by which our present knowledge has been reached. 



With regard, for instance, to the physiology of the circula- 

 tion, it is not only curious but instructive to follow its gradual 

 growth from Galen and Vesalius, Columbus, C^salpinus, and 

 Servetus, to Harvey and Lower and Malpighi, to Hales and 

 Vierordt, to Ludwig, and Chauveau, and Gaskell, and Roy. 

 The only true scientific method is the historical one. If we 

 only know the results of a science without the steps by which 

 they have been reached, we have indeed its practical use, but 

 lose half its educational value. We are almost in the position 

 of an engineer who knows the conclusions of trigonometry by 

 rot«, but is ignorant of the demonstration. I would therefore 

 urge upon junior Fellows, while still enjoying the prospect 

 rather than the fruition of professional success, to spare some 

 of the time which is unoccupied by work in wards and labora- 

 tories for the perusal of such antiquated works as have been 

 published as much as twenty years ago, and particularly for 

 gaining acquaintance at first hand with classics like Virchow's 

 " Cellular Pathology," and the lectures of Watson, Trousseau, 

 and Stokes ; or, if their time and inclination does not allow of 

 more extended researches, at least to read such succinct master- 

 pieces as Laennec's "Mediate Auscultation," Heberden's 

 "Commentaries," Sydenham's "Treatise on Gout," and 

 Harvey " On the Movement of the Heart and of the 

 Blood." 



(3) I would, moreover, exhort Fellows of the College to 

 see that, while all the new methods of experimental pathology 

 and pharmacology are carried out by duly trained physiologists, 

 we do not neglect the fundamental method taught and practised 

 by Harvey of inspecting the bodies of those who have died of 

 disease. It was this union of morbid anatomy with clinical 

 observation which made the discoveries of Laennec and of 

 Bright really fruitful. Without these autopsies, clinical medi- 

 cine is but an empirical art, diagnosis a sham, and treatment 

 little better than quackery. Exclusive attention to therapeutics 

 is apt to bring a man dangerously near to homeopathy and 

 other pretended systems of treatment, but sound pathology, and 

 diagnosis controlled by post-mortem inspection, give positive 

 knowledge and that union of modest self-confidence and prudent 

 enterprise which become the physician. 



Lastly, I have to fulfil the duty of exhorting the Fellows of 

 this ancient College ' ' to continue in mutual love and affection " 

 among ourselves ; and this is the easiest task of all. For, if 

 we must admit that experimental science in England, and par- 

 ticularly scientific pathology, is not surpassing our byegone 

 achievements as it ought to surpass them, considering the in- 

 creased number of competent labourers and the vastly improved 

 methods of research ; and if we admit that the crowd of modern 

 literature, and the distractions which we fondly imagine to be 

 peculiar to our generation, leave small opportunity for the culti- 

 vation of ancient learning ; and if the prejudices of our 

 patients, both gentle and simple, still make post-mortem 

 inspections less common and systematic than they should be — 

 whatever, I say, may be our shortcomings in these or in other 

 respects — your Harveian orator may most honestly congratulate 

 the College and the profession upon the concord and mutual 

 esteem which has happily marked our history from the days of 

 Linacre to those of Harvey, from the days of Arbuthnot and 

 Garth to those of Meade and Freind, from the days of Fothergill 

 and Heberden to those of Matthew Baillie, of Babington, and of 

 Sir Thomas Watson. Long may this continue, for thereon de- 

 pend not only the dignity and peace of our profession, but in great 

 measure our power of doing good. However ignorantly our pa- 

 tients will sometimes decry what they call professional etiquette, 

 the wiser among them know (and in the long run the wise lead the 

 foolish) that this term really means the observance of the rules 

 which distinguish a profession from a trade, which make our 

 calling honourable as well as honest, which check the arts of 

 advertisement and direct our ambition to obtaining the suf- 

 frages, not of the public which cannot, but of our profession 

 which can, judge truly — rules of conduct which are, in fact, 

 nothing but the carrying into daily practice of the golden rule to 

 do to others as we would they should do to us. For maintaining 

 and strengthening this spirit of concord and good feeling, we 

 depend upon each one of our Fellows, but especially on the 

 example and authority of our Head — an example and authority 

 which, as the College well knows, are worthily maintained 

 by the untiring devotion to its best interests of our honoured 

 President. 



NO. I 25 I, VOL: 48] 



THE EFFECT OF WATER VAPOUR ON 

 ELECTRICAL DISCHARGES. 



A VERY interesting paper by Prof. J. J. Thomson, 

 "^ on the effects of electrification and chemical action on a 

 steam jet, and of water vapour on the discharge of electricity 

 through gases, appears in the October number of the Philo- 

 sophical Magazine. In it the author first considers the effect of an 

 electrical field on the surface tension of a water drop, and he 

 shows that if the electrical field is uniform, the diminution in 

 the surface tension is very small and independent of the size of 

 the drop ; so that a uniform field will not be able to counter- 

 balance the effect of surface tension, since the latter varies 

 inversely as the radius of the drop, and therefore when the drop 

 is excessively small must be greater than the constant effect due 

 to the electric field. When, however, the electric field instead 

 of being uniform is due to a number of charged atoms distri- 

 buted throughout the volume occupied by the steam, the effect 

 of the electric field in diminishing the surface tension varies 

 inversely as the square of the radius of the drop. Thus for very 

 small drops the electrification will overpower the cause (surface 

 tension) which, under ordinary circumstances, puts an end to 

 the existence of small drops. The above seems capable of 

 explaining the effects of electrification on a steam jet first 

 observed by Helmholtz, for the electricity which escapes into 

 the gas is carried by charged atoms of the gas, and since in the 

 region immediately around these atoms there will be a very 

 intense electric field there will be a tendency for the steam to 

 condense into drops in these regions. Helmholtz also dis- 

 covered that chemical action in the neighbourhood of the jet 

 affected it in much the same way as a discharge of electricity. 

 If the forces which hold the atoms together in a molecule are 

 electrical in tlieir origin, so that in a diatomic molecule one 

 atom has a positive and the other an equal negative charge, the 

 above explanation will also apply to this case. For when the 

 molecule of the gas is in the ordinary state, the equal and op- 

 posite charges of the atoms will, in the region outside the mole- 

 cule, neutralise each other's effect, so that the electrical field 

 round a molecule will be much less intense than that round a 

 single charged atom, and thus, though the field round the latter 

 may be sufficient to cause condensation, that round the molecule 

 may not. When, however, the molecules which enter into 

 chemical combination come together and form a new compound, 

 requiring a rearrangement of the atoms, then while the chemical 

 change is going on, there will be an interval during which the 

 atoms are comparatively free, and there will be an electric field 

 almost as strong as if the atom were dissociated. 



The author also considers the effect of moisture in promoting 

 chemical action, for if the forces which hold the- atoms in the 



molecule together are electrical in their origin it is evident that 

 these forces will be very much diminished when the molecule 

 is near the surface of, or surrounded by, a conductor or a sub- 

 stance like water having a high specific inductive capacity. 

 Thus if A and B represent two atoms in a molecule placed near 

 a conducting sphere, then the effect of the electricity induced on 

 the sphere by A will be represented by an opposite charge placed 

 at the image of A in the sphere. If A is very near the sphere, 

 this opposite charge will be very nearly equal to that at A. 

 Thus theeflfect of the sphere will be to practically neutralise the 

 electrical effects of A, and as one of these effects is to hold the 

 atom B in combination, the affinity between the atoms A and B 

 will be almost entirely annulled by the presence of the sphere. 

 Molecules condensed on the surface of a drop of water or sur- 

 rounded by water will thus be practically dissociated, or at any 

 rate the forces between their component atoms will be much 

 reduced. Since water vapour produces so great an effect on 

 chemical combination, it is interesting to investigate whether its 

 presence has any considerable influence on the passage of elec- 

 tricity through gases, since there is strong evidence that this 

 phenomenon is closely connected with chemical changes taking 

 place in the gas through which the discharge takes place. 

 Observations were made on dry and damp hydrogen, and show 

 that there is a marked difference both in the appearance of the 

 spark and in the proportion between the potential difference 

 necessary to produce the first spark through the gas, and that 

 which is sufficient to cause one to follow it immediately after- 

 wards. In the damp gas this difference was comparatively 

 small, averaging about ten per cent. In the dry gas, however, 

 this effect attains quite abnormal proportions, the potential 

 difference required to produce the first spark being often more 



