402 



NATURE 



[February 27, 1902 



On development and measuring the resulting images, the 

 following figures were obtained : — 



Circle over cell A — Opacity log. = -342 ; Opacity = 2 '20. 



Circle over cell B — Opacity log. = '178; Op.icity = I '51. 



Circle over cell i— Opacity log. = '025 ; Opacity = 'li. 

 Ratio b/a = '68. 



It thus appears that a current of air passed over the surface 

 of a radium compound carries with it a certain proportion of the 

 corpuscles. This is proved by the diminished photographic 

 action in the second cell, slightly confirmed by the evidence that 

 some few of the corpuscles so carried away get to the sensitive 

 film on cell c. Judging from our slender knowledge of the 

 properties of free electrons, it is highly probable that they will 

 not easily turn a corner, but cling to the sides of the tube 

 through which they are being led. On the other hand, the 

 constant collisions with the atoms of air may reduce their initial 

 mobility almost to a vanishing point before they have travelled 

 along the lube between B and c, and then they would be carried 

 along with the air. 



The experiment was repeated, using a preparation of actinium 

 (Uranium X). It was kept going for seventy-two hours, during 

 which time 750 litres of air were drawn through the apparatus. 

 On development and measurement, the following results were 

 obtained : — 



Circle over cell A — Opacity log. = '99 ; Opacity = 978. 

 Circle over cell B — Opacity log. = '67 ; Opacity = 4'6S. 

 Circle over cell c — Opacity log. = '25 ; Opacity = i 78. 



Here then the results agree with those tried with radium 

 compounds ; that corpuscles are carried by a current of air from 

 cell B, through the connecting tube to cell c. They also confirm 

 those of Dr. kutherford — who finds that thorium emanations 

 travel in a current of air while retaining their activity — and of 

 P. Curie and A. Debierne, who show that induced radio-activity 

 can be transmitted through capillary tube.s, of an internal 

 diameter of i mm. and 75 cm. in length, bent once at right 

 angles. 



I have not obtained, however, a similar result with the 

 emanations from hydrogen peroxide. As shown by Dr. Kussell, 

 this substance has a strong action on a sensitive photographic 

 plate. The emanation from a bottle half full of hydrogen 

 peroxide acts strongly on a sensitive film laid over the open 

 mouth of the bottle for twenty-four hours, while there is no 

 action in seventy-two hours if a U-shaped tube passed through 

 the cork of the bottle and the sensitive film is put close to the 

 open end of the tube. Dr. Kussell tells me his observations 

 confirm my experiments. 



A highly active self-luminous radium compound loses some of 

 its power on long exposure to the ordinary air of the laboratory. 

 When enclosed in glass, the glass soon assumes a pink colour. 

 If, however, the radium compound is sealed in vacuo in a quarlz 

 tube, no coloration takes place, and I can detect no diminution 

 of energy even in twelve months. 



Electrons from radium will pass through aluminium and a 

 considerable length of air and affect a sensitive film.' Experi- 

 ments on this point were tried with polonium, and it was found 

 that air offered great obstruction. 



The electron theory explains a fact which has long puzzled 

 experimentalists. It is well known that if a coin is laid on a 

 sensitive plate in perfect darkness and connected with one pole 

 of an induction coil for a few seconds and then developed, an 

 image can be obtained of the raised parts of the coin. This 

 has generally been explained by saying that the electrified 

 stream of air, or the "brush discharge," affects the film like 

 light. 



But Mr. F. Sanford (Naturi;, vol. Iv. p. 485) shows that 

 coins embedded in the centre of a block of paraffin 2 cm. thick, 

 where they could not send off streams of electrified air, can still 

 be photographed by means of the induction coil. In these 

 circumstances it is probable that electrons are the agents, as 

 electrons will easily pass through parafiin wax from the coin to 

 the sensitive plate, when the coin is connected with the negative 

 pole of an induction coil, the other pole being connected with a 

 metal plate placed below the wax block. 



, I have obtained an impression on 



* Using an active compound of radiu 

 ""ive film, througti a penny-piece. 



NO. 1687, VOL. 65] 



Hitherto we have been dealing with negative electrons — a free 

 positive electron at present is unknown. In a paper communi- 

 cated to the Royal Society, December, 1890 {Phil. Trans., 

 1901, A, vol. cxcvi. p. 525), the Hon. R. J. Strutt offers a sug- 

 gestion as to positive ions which in a satisfactory manner appears 

 to explain much that hitherto has been left doubtful, not to say 

 contradictory. 



He adopts the generally recognised theory that the deflectable 

 Becquerel rays consist of a stream of negative corpuscles with 

 enormous velocities proceeding from the radio-active body. 

 But there are two kinds of Becquerel rays, one deflectable and 

 penetrating, the other non-deflectable and easily absorbable. 

 Mr. Strutt considers that these non-deflectable rays are positive 

 ions moving in a stream froin the radio-active body. 



He says: — "We know that the posilive ions in gases carry 

 the same charge as the negative, and that they have an enor- 

 mously greater mass. Unless, therefore, their velocity is smaller 

 out of all proportion than the negative ions, it is to be expected 

 that they will be much less easily deflected by the magnet. . . . 

 Next it may be noticed that the smaller penetrating power 

 would be well accounted for by the size of the positive 

 ions, which would, of course, make more collisions with 

 the molecules of the surrounding gas than the much smaller 

 negative ions." 



Of the three radio-active bodies, radium, actinium and polo- 

 nium, actinium appears to emit corpuscles almost entirely of the 

 penetrating, deflectable kind, polonium rays of the non-deflect- 

 able, non-penetrating kind, whilst radium emits rays of both 

 kinds. 



On the above hypothesis, corpuscles from polonium might 

 consist of the heavy positive ions : to test the accuracy of this 

 inference experiments are now in progress. 



Some curious and far-reaching inferences may be drawn from 

 Mr. Strutt's view, supposing it to be correct, that positive as 

 well as negative corpuscles will fly off from a radio-active body. 

 In a paper " On Electrical Evaporation " {Koy. Soc. Proc, vol. I. 

 p. 88, June, 1891) I showed that many bodies, such as silver, 

 gold, platinum, &c. , usually considered non-volatile at ordinary 

 temperatures, easily volatilise in a vacuum if connected with 

 the negative pole of an induction coil, remaining fixed when 

 connected with the positive pole. This phenomenon was first 

 observed by Dr. Wright, of Vale College, and was applied by 

 him for the production of mirrors for physical apparatus. It 

 is shown by experiments that the action in the vacuum tube is 

 of two kinds. A silver pole was used, and near it, in front, 

 was a sheet of mica with a hole in its centre. The vacuum was 

 very high (P = 0'OOo68 mm.), and when the poles were con- 

 nected with the coil, the silver being negative, electrons shot 

 from it in all directions, and passing through the hole in the 

 mica screen, formed a bright phosphorescent patch on the 

 opposite side of the bulb. The action of the coil was continued 

 for some hours, to volatilise a certain portion of the silver. On 

 subsequent examination it was found that silver had been de- 

 posited only on the mica screen and in the immediate neighbour- 

 hood of the pole, the far end of the bulb, at the spot which 

 had been glowing for hours from the impact of electrons, being 

 free from silver deposit. Here then are two simultaneous actions. 

 Electrons, or, as I once called them, " radiant matter," shot 

 from the negative pole and caused the glass against which 

 they struck to glow with phosphorescent light. Simultaneously 

 the heavy positive ions of silver, freed from their negative 

 electrons, or under the influence of the electrical stress, like- 

 wise flew off, and were deposited in the metallic state near 

 the pole. 



During the course of iny experiments a curious circumstance 

 was observed, which deserves record as it may elucidate some of 

 these obscure phenomena. While the volatilisation of the silver 

 pole is rapidly proceeding, the metal gUnvs as if red-hot. This 

 " red heat " is superficial only. The metal instantly assumes, or 

 loses, the appearance of red-heat the moment the current is 

 turned on or off, showing that the high temperature does not 

 penetrate below the surface. The volatilisation of the positive 

 ions is confined to the surface and the surface glow is connected 

 with that action. If instead of silver, a good conductor of 

 heat, I take diamond, a bad conductor, the surface layers 

 are changed sufiiciently to convert them into a form of 

 graphite, which from its great resistance to oxidising agents 

 cannot have been formed at a lower temperature than 

 3600° C. 



