454 



NA TURE 



[September 8, 1904 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he undertake 

 to return, or to correspond ivith the writers of, rejected 

 iimmiscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous coinmimications.] 



On the Secondary Radiation due to the 7 Rays of 

 Radium. 



In a recent communication to the Annalen der Physik 

 (4 and 5, 1904), Paschen described experiments show- 

 ing that a thiclc lead block containing radium emits 

 negatively electrified particles which can be deviated in a 

 magnetic field. He concluded that he had deflected the 

 7 rays, thus differing from previous experimenters. 



I have found that particles having a negative charge 

 are projected, and are readily deflected magnetically. How- 

 ever, these are not y rays, but differ from them inasmuch 

 as they are completely absorbed by about a millimetre of 

 lead. 



In order to prove this, an electroscope with a thin 

 aluminium face was mounted on a lead platform (12 cm. 

 tliick) above a block of lead 10 cm. high, at the centre of 

 which was placed 30 mg. of radium. On applying a 

 magnetic field to bend the rays towards the electroscope, 

 the electroscope readings were doubled, but this increase 

 was reduced to half value by a screen of lead (01 mm. thick) 

 placed in front of the aluminium face. Since negatively 

 charged particles are thus projected from the lead surface, 

 it is clear that, as Paschen observed, a block of lead, placed 

 in a vacuum and well insulated, would acquire a positive 

 charge, and would continue to do so as long as the radium 

 emitted 7 rays, even if these penetrated two or three inches 

 of lead. 



The effect which Paschen observed was due not to the 

 primary 7 rays, but to the diffuse secondary radiation 

 caused by the 7 rays in the lead. This may be shown to 

 be mainly a surface effect, for the secondary radiation from 

 a greater depth than one or two millimetres is absorbed by 

 the lead itself. The curvature of the rays, necessarily implied 

 by Paschen 's second experiment, is so large that other ex- 

 perimenters could not have failed to detect it by direct 

 methods had the effect been due to 7 primary rays. 



This deflection of 7 secondary radiation by a magnetic 

 field is similar to Becquerel's result, obtained photo- 

 graphically, when he deflected the ;8 secondary rays. Curie 

 and Sagnac have also shown that Rdntgen rays striking 

 a metal cause it to emit negative electricity and to acquire 

 a positive charge ; Dorn has proved that such rays can be 

 deflected by a magnet. 



.■Kny experiment designed to prove that the primary 7 rays 

 can be affected by a magnetic field must involve evidence 

 that the effect produced is not due to the easily deviated 

 7 secondary radiation. A. S. Eve. 



McGill University, Montreal, August 22. 



A Source of the lonisation of the Atmosphere. 



It is perhaps not very generally known that human 

 breath has a considerable power of discharging an electrified 

 conductor. This fact can be strikingly shown by an ex- 

 periment easily carried out. If the discharging knobs of a 

 Wimshurst electrical machine are drawn apart so far that 

 a spark just refuses to pass, then on breathing across the 

 gap the spark is instantly precipitated. 



The discharging power of the breath is more conclusively 

 demonstrated, however, by breathing through a metal tube 

 into which an insulated metal rod projects a.xially, the 

 insulation of the rod being out of reach of the breath. If 

 the rod is connected to the cap of a graduated gold-leaf 

 electroscope, comparative observations show that the rate 

 of discharge of the electrified rod and gold leaves is 60 per 

 cent, to 70 per cent, greater when air from the lungs is 

 passing through the tube than when ordinary air fills it. 

 Again, the rate of leak of a charged electroscope in a 

 small, badly ventilated class-room, was found to be 50 per 

 cent, more rapid when the room was full of students than 

 when it was empty. Incidentally, this explains in part 

 why experiments on electrostatics are often troublesome to 

 carry out in a room crowded with a large audience. 



NO. 18 19, VOL. 70] 



The point of interest, however, in these experiments is 

 the fact that the slow low-temperature combustion going 

 on in the lungs ionises the air in the same way as the rapid 

 high-temperature combustion of flames. And if this slow 

 ionisation of the air can take place in the lungs of living 

 animals, it may also go on less markedly in the chemical 

 interaction between the air and living plants, and in some 

 cases between the air and inorganic matter, at ordinary 

 temperatures, so that there is here a continual source of 

 atmospheric ionisation apart from any possible radio-active 

 processes. J. R. Ashworth. 



Rochdale, August 27. 



Celtic Place-names. 



The review of Mr. Johnston's " Place-names of Scot- 

 land " in your number of July 28 explains a problem that 

 has been for a long time a puzzle to me in reference to the 

 existence in County Leitrim alone, of the thirty-two counties 

 in Ireland, of the word " allt " in common parlance. 



To North Leitrim there came over from Stirlingshire 

 about the year 1608, as followers and soldiers of Sir 

 Frederick Hamilton, grandson of the second Earl of Arran, 

 a strong Scotch colony. From them we took in a great 

 measure our English or Scotch-English. Here is a trace 

 of it. A half-dozen others of our distinctive Leitrimisms I 

 have already traced back to Scotland ; others to elsewhere. 



In odd words and odd uses of them, and in odd pro- 

 nunciations, are found " helpful and interesting sidelights 

 for the historian " (to use the reviewer's expression) all 

 through Ireland. Indeed, the " Irish plantations," and the 

 parts of England and of Scotland the planters came from, 

 might be plotted out by a careful observation of such 

 peculiarities. They are disappearing. Before it is too 

 late, or it becomes too difficult, it would be well worth 

 while for someone who knows the rural districts of both 

 countries intimately to attempt the task. It should well 

 repay the historian or the philologist. I have been trying 

 something like it, but I have had slight opportunity for 

 making the acquaintance of any English dialects except the 

 Yorkshire and the Lancashire, and I cannot accordingly 

 push it very far. 



I have to thank the reviewer ; but permit me to say that 

 the Leitrim use of " allt " (or " alt ") corresponds rather 

 with that given by Mr. Johnston than with that claimed 

 by him. With us an " alt " is not " a streamlet passing 

 through a ravine," but a narrow, deep glen or hollow 

 through which, as a rule, of course, a stream or streamlet 

 flows; but that a stream should do this is not essential for 

 the chasm to be so termed. Joyce, too, would support this. 

 The word alt, he states (" Irish Names of Places," p. 353, 

 i86g edition), is found in townland names in Ireland, and 

 in its topographical application it is generally understood 

 to mean a cliff or the side of a glen. 



I should be much interested in knowing if Mr. Johnston 

 would subscribe to our precise application of the word. It 

 is evidently a primitive word of Aryan origin. The meaning 

 of all allied words in any language I am familiar with 

 favours our interpretation, and it is hard to see how it 

 could come by the meaning of " streamlet," however 

 flowing. Joseph Meehan. 



Creevelea, Drumkeeran, Co. Leitrim, August 5. 



I HAVE read with much Interest your correspondent's letter, 

 and can well understand his difficulty with regard to the 

 Scottish usage of the word allt. Here it is applied, as I 

 have stated, to a stream passing through a ravine or hollow ; 

 never, so far as I am aware, to a glen or dry chasm. 



The Irish alt, which is slightly different in spelling, is 

 also apparently different in application. Your correspondent 

 may be interested in the various Celtic usages of the word 

 as given bv Dr. Macbain in his " Etymological Dictionary 

 of the Gaelic Language " : 



"Allt, a stream; Ir. alt, height, (topographically) glen- 

 side or cliff; O. Ir. alt. shore, cliff; O. W. allt, cliff; 

 Cor. als ; Br. aot, shore, all allied to Lat. altus. The Gaelic 

 form and meaning are possibly of Pictish origin." 



Looking down or up the precipitous sides of many a 



