278 



NA TURE 



[January 6, 19 10 



LETTERS TO THE EDITOR. 



[The Editor docs not hold liimself responsible for opinions 

 expressed by his correspondents. Neither can he undertake 

 to return, or to correspond -with the writers of, rejected 

 manuscripts intended for this or any other part o/ Nature. 

 No notice is taken of anonymous commtmications.] 



The Heat developed during the Absorption of Elec- 

 tricity by Metals. 



In 1901 (O. W. Richardson, Canib. Phil. Proc, vol. xi., 

 p. 286J one of the present writers showed that the pheno- 

 mena attending the emission of negative electricity by liot 

 metals could be explained on the assumption that the 

 electrons which, on the electron theory of metallic conduc- 

 tion, move freely inside the metal attain sufficient kinetic 

 energy at high temperatures to enable them to overcome 

 the forces tending to keep them inside the surface and so 

 escape. From the way in which the thermionic current 

 varied with the temperature of the metal it was shown 

 that the difference in the value of the potential energy of 

 an electron when outside and when inside a metal could 

 be calculated. Somewhat later (O. \V. Richardson, Phil. 

 Trans., A, vol. cci., p. 497) it was shown that the existence 

 of this difference in the potential energies would involve 

 a loss of thermal energy by the substance when the electrons 

 were being given off, and it was pointed out that this 

 effect would increase very rapidly with the temperature, so 

 that at sufficiently high temperatures the loss of energy 

 due to this cause would be greater than that arising from 

 thermal radiation. An effect of this character has recently 

 been discovered by Wehnelt and Jentzsch {.inn. der Physik, 

 iv., vol. xxviii., p. 537). 



Another consequence of the existence of this difference of 

 potential energy is that when electrons possessing negligible 

 kinetic energy pass into a metal an amount of heat should 

 be liberated which is equal in magnitude to the difference 

 in the potential energy for each electron multiplied by 

 the number of electrons entering the metal. Experi- 

 ments which have been carried out by the writers 

 show that this effect exists, and is of the expected order 

 of magnitude. 



The method adopted was to cause the electrons emitted 

 by two hot osmium filaments to flow on to a grid of fine 

 platinum wire, which acted as a bolometer, and was placed 

 in one arm of a double Wheatstone's bridge. The double 

 bridge arrangement enabled the galvanometer to be balanced 

 for the thermionic current into the bolometer in each 

 experiment. The change in the resistance of the bolometer 

 per unit thermionic current was measured when different 

 voltages were maintained between it and the negative ends 

 of the filaments. 



In order to standardise the bolometer a known variation 

 of current through it was produced, and the resulting 

 change of resistance due to heating measured. By making 

 use of this datum the energy received by the bolometer 

 per unit thermionic current can be expressed in terms of 

 the fall of potential which the electrons would have to 

 undergo in order to produce the observed effect. The value 

 thus obtained may be denoted by the " effect in volts." 



When the effect in volts E is plotted as ordinate against 

 the negative potential of the negative end of the filaments 

 V as abscissa, the relation between them appears to be 

 a linear one. The line, however, which is obtained does 

 not intersect the axis of ordinates at E = o, but in the 

 neighbourhood of E = 3 volts, showing that when the 

 electrons fall through no difference of potential due to the 

 field they are still able to produce a heating effect equiva- 

 lent to that due to the energy they would have received 

 in falling through a difference of potential of about 3 volts. 

 Inasmuch as Richardson and Brown [Phil. Mag. [6], 

 vol. xvi., p. 353) have shown that the natural kinetic 

 energy with which the thermions are emitted corresponds 

 to only about 1/30 volt, the conclusion is inevitable that 

 there is a liberation of potential energy when the electrons 

 enter the metal comparable with that which would be 

 acquired by falling through a difference of potential of 

 about 3 volts. 



Experiments have, so far, been made with applied 

 potentials varying from +2 to —9 volts, the potential drop 

 NO. 2097, VOL. 82] 



along the filaments due to the heating current varying 

 from 3 to 3-7 volts. Changes are now being made in the 

 experimental arrangements which, it is believed, will lead 

 to greater accuracy of measurement. It seems likely 

 that, owing to certain defects in the present apparatus, the 

 values which have so far been obtained are somewhat too 

 low. O. W. Richardson. 



H. L. Cooke. 

 Palmer Physical Laboratory, Princeton University, 

 Princeton, N.J., December 21, 1909. 



Malaria and Ancient Greece. 



In his scholarly " Malaria and Ancient Greece," re- 

 viewed in Nature of December 16, 1909, p. 192, Mr. 

 Jones has apparently overlooked what seems to be, though 

 modified for dramatic purposes, a description of an acute 

 attack of ague, i.e. that given by Sophocles of the suffer- 

 ings of Philoctetes in his play known by that name. Here, 

 just' as he is about to accompany Neoptolemus to the ships, 

 Philoctetes is seized with a sudden attack (line 730). He 

 recognises the prodromal symptoms of what he describes 

 to Neoptolemus as a recurrent attack of his malady 

 (iiK€i yap avTTi 5ia XP'^'"'"' ''"6 758). The attack appears 

 to be ushered in with pain or discomfort (line 730) and 

 shivering (735). The symptoms become increasingly acute 

 {Kai Ti TrpoaSoKii vfov, 784) until they become almost un- 

 endurable (790). Soon, however, from previous experience, 

 Philoctetes can foretell that the worst is over (808), and 

 that the attack will pass away during the sleep which 

 always supervenes. \aii$dvfi yap oiv Siryos fx, oToi' irep rh 

 KOKif fliiri r6Se, 766. 



Later on, as he is falling asleep, Neoptolemus directs 

 the attention of the Chorus to the profuse perspiration 

 which bathes his body (823). The periodicity, suddenness, 

 and ingravescence of the symptoms, the sleep and sweat- 

 ing followed by a passing feebleness on waking (880), 

 present a clinical picture the vividness and truth of which 

 are not surpassed in any literature. The congeries of 

 symptoms in this description must be based upon actual 

 experience of disease. It will, of course, be urged 

 that Sophocles makes all the symptoms dependent upon 

 the uncured wound in the heel caused by the snake-bite 

 at the shrine of Chryse. Here there need be, however, 

 no difficulty in the acceptance of the ague theory, for 

 this would be in full accord with the accepted pathology 

 of the period. The Greek physicians were probably well 

 acquainted with the characteristic results of non-fatal 

 snake-bite — the pain, sloughing with foul discharge, and 

 delayed healing. 



Without attempting to labour the point further, from a 

 strictly clinical point of view the imposition of a malarial 

 infection upon a chronic condition such as that described 

 would, without doubt, give rise to periodic exacerbations 

 of the inflammatory conditions. This is probably the 

 explanation of the statement of Hippocrates quoted by 

 Arndt [cp. Jebb, Philoctetes, p. 241) that the " ulcers 

 become especially inflamed on these alternate days." 



The Philoctetes was performed in 409 B.C., just when, 

 according to Mr. Jones's theory, malaria was becoming 

 widely disseminated through Greece, and nothing would 

 be more natural than that Sophocles, in his wish to draw 

 the sympathies of his audience to his long-suffering hero, 

 should represent him as wracked with all the horrors of 

 the new and strange disease, which appeared to lend them- 

 selves peculiarly to his purpose. There can scarcely be a 

 sight more pitiable than that of a person in an acute 

 paroxysm of malaria. 



It is much to be regretted that the loss of their re- 

 spective plays prevents a comparison with the manner in 

 which ,4ischylus and Euripides treated the subject. That 

 Sophocles had a keen clinical grasp of the salient features 

 of disease is noticeable in his description of the .'\cute 

 Delusional Insanity of .\jax — a description of a form of 

 mental aberration which is extraordinarily true to nature, 

 and one which from a clinical standpoint far surpasses 

 the delineations of madness by Shakespeare, as might 

 indeed be expected from a consideration of the relative 

 positions of medicine as a science at the times of the re- 

 spective poets. George A. Auden. 



Birmingham. 



