NA TURE 



[November 4, 1909 



exceedingly important, and Sir \V. Ramsay lias given 

 reasons for believing that the capillary behaviour of 

 mercury is quite abnormal in the presence of emanation. 

 Another serious difficulty with which we had to contend 

 was that, under the action of the emanation, the silver 

 (or platinum) through which the light had to pass gradually 

 became opaque. The consequence was that the apparatus 

 had each time to be dismounted after a couple of days, 

 the faces re-polished, re-silvered, and re-installed before 

 a new experiment could be begun. This source of incon- 

 venience would, of course, not be present in apparatus 

 similar to the Young-Arago method employed by Lord 

 Ravleigh or in a Jamin refractometer (which we think 

 is the more satisfactory of the two), but we do not think 

 that it would be possible to obtain an equal optical 

 efficiency with these arrangements. 



The amount of success attending these experiments — 

 small though it may seem to be — justifies us in hoping that 

 if the amount of available emanation were increased a 

 few times only an approximate value of the refractivity 

 would be ascertainable. Even at the present time this 

 might be effected by means of a collaboration amongst all 

 those in the United Kingdom who possess large quantities 

 of radium. 



In conclusion, we desire to express our thanks to Sir 

 \V. Ramsay for generously supplying us with the emana- 

 tion with which these experiments were made. 



Alfred W. Porter. 

 Clive Cutiibertson. 



Physical Department, l"nivirsity College, London, 

 November i. 



Atmospheric Cloudy Condensation. 



In Nature of October 21 Sir Oliver Lodge, writing 

 on the recent magnetic storm, seems to think that during 

 these storms the sun is emitting electric projectiles which 

 cause the magnetic disturbance, and that these projectiles 

 will, at the same time, affect the rainfall by the influx of 

 " cosmic nuclei." From this, 1 presume. Sir Oliver 

 means that the electrons passing through our atmosphere 

 will produce ions in the air, and that these ions will 

 become nuclei of condensation, and in this manner may 

 increase temporarily and locally the rainfall. Now, so far 

 as is at present known, it does not seem probable that 

 these electrified nuclei play any part in cloudy condensa- 

 tion. That they can become centres of condensation is 

 not doubted, but before they can act in that way the 

 atmosphere has to become very highly supersaturated. 



These ions, therefore, cannot play any part in the con- 

 densation unless all the dust in the air be first removed. 

 The question thus becomes, Is there such a thing as dust- 

 tree air in our atmosphere? So far as I am aware, no 

 such condition has ever been observed. I have returns 

 of observations made in many parts of the world by 

 different observers, as well as by myself. Some of these 

 tests were made while crossing the Atlantic Ocean, others 

 on the Pacific Ocean. Many were made in this country 

 and in different countries on the Continent. Some were 

 made at sea-level, others up to an elevation of 13,000 feet, 

 but none of these records shows anything like dust- 

 less air. Mr. Rankin, in his Ben Nevis report, says " any 

 number less than 100 particles per cubic centimetre is 

 phenomenally small." Mr. E. D. Fridlander, at an eleva- 

 tion of more than 13,000 feet on the Bieshorn, found 157 

 particles per c.c. In many hundreds of observations made 

 by myself on the Rigi Kulm (6000 feet) nothing quite so 

 low as 200 per c.c. was ever observed. The reports of the 

 observations made on the oceans show the dustv air to be 

 everywhere, and there does not seem to be much chance 

 ot ever finding dustless air, at least so low as cloud-level, 

 as the air with least dust is not found in the descending 

 currents of anticyclones, but in the cyclonic areas, where 

 the air is well washed by the rains. It may be further 

 stated, in connection with this subject, that there is no 

 reason for supposing that an increase in the number of 

 nuclei would have any effect on the rainfall, as in nature 

 only a few of the nuclei do all the condensation, while 

 the others remain inactive. 



This letter may seem longer than the subject warrants, 

 but my reason for entering so fully into the subject is 

 NO. 2088, VOL. 82] 



that the idea is now very generally accepted that ions do 

 form the nuclei of cloudy condensatio,n in our atmosphere. 

 So stereotyped has this theory become that there is not a 

 scientific book recently published in which this subject is 

 treated which does not give this view. Now, so far as 

 our knowledge at present goes, there is no support for 

 this theory, and those who advocate it will require to 

 show that there is ever dustless air at cloud-level. I have 

 elsewhere shown that, even supposing there was dust-free 

 air, clouds would not likely be formed, but "the super- 

 saturation would be relieved by the direct formation of 

 rain, as the condensation in the highly supersaturated air 

 would take place on only a few nuclei, which would grow- 

 very rapidly to rain-drops. 



It is not here contended that the passage of the electrons 

 through our atmosphere will have no effect on the rain- 

 fall, only that it has not been shown that there are ever 

 the conditions necessary for the ions so formed to act as 

 nuclei of cloudy condensation. That the electrons may 

 act in some way in determining the coalescence of cloudy 

 particles to form rain-drops seems possible, but, so far as 

 I am aware, even this has not been demonstrated. 



Ardenlea, Falkirk. John Aitken. 



Magnetic Storms. 



J'ai lu avec le plus grand int^ret dans le No. 2083 de 

 ce p^riodique la note importante de M. le docteur Chree 

 sur la dernifere grande perturbation magn^tique du 

 25 septembre, 1909. 



Comme je fais depuis 1882, j'ai cherch^ de la mettre 

 en relation avec le passage de la grande tache solaire 

 australe qui a ^t^ observ^e, dessin^e et relev^e k I'observa- 

 toire de Catane par I'assistant M. L. Taffara tous les 

 jours depuis 1 'apparition au bord est le 18 septembre 

 jusqu' k la disparition au bord ouest le 29 septembre, 

 except^ les jours 19 et 22, ou I'observation a ^t^ empech4e 

 par les nuages. 



De nos observations il resulte que la tache doit §tre 

 passive par le miridien central le 23 septembre, environ 

 k 5h. soir, temps moyen de Greenwich. 



Dans la relation de M. Chree n'est pas donn^ le temps 

 du maximum de la perturbation, parceque les oscillations 

 des appareils magn^tiques de I'observatoire de Kew 

 etaient souvent plus amples de ce que pouvaient 6tre 

 cnregistr^es. En considirant le commencement et la fin 

 des oscillations plus amples, on a les temps iih. 43m. et 

 Sh. 30m. et la moyenne 4h. 7m. 



Si I'on fait la difference avec le temps du passage de la 

 grande tache, c'est a dire sept. 25, 4h.-sept. 23, sh.= 

 ij. 23h. = 47h., on a le retard de la perturbation mag- 

 netique sur le temps du passage de la tache k la moindre 

 distance du centre du disque solaire, c'est i dire k la 

 moindre distance de la droite qui unit le centre du soleil 

 i la terre. 



Ce retard est trfes pcu different de celui de 45 Jh. que j'ai 

 trouv^ en moyenne pour 8 coincidences de passages 

 de grandes taches avec le maximum de fortes perturba- 

 tions magnitiques du premier semestre 1892 ; ce retard 

 aussi n'est pas trop diff(?rent de celui dc 42.5h. que j'ai 

 trouviJ entre le temps moyen du commencement et de la 

 fin de 19 grandes perturbations magn^tiques et le temps 

 des passages de grandes taches, ou de grands groupes de 

 taches, d'aprfes les rel^vements de M. Maunder de 

 I'observatoire de Greenwich. 



II serait done confirm^ aussi pour cette grande per- 

 turbation magndtique un temps de 40 k 50 heures pour 

 la propagation du soleil h. la terre de I'influence ou action 

 solaire sur le magn^tisme terrestre ; ce qui don- 

 nerait une vitesse de 900 k 1000 km. par seconde ; c'est 

 k dire une action plus que 300 fois moindre de celle de 

 la lumiire et des actions ^lectromagn^tiques. Mais cette 

 Vitesse pourrait bien 6tre celle des particules ^mises par 

 le soleil, selon les id^es de M. Arrhenius. 



Ainsi I'hypot^se corpusculaire de I'influence solaire 

 acQuiert toujours une plus grande probability. 



L'assistant M. le Dr. Horn a fait k I'observatoire de 

 Catane prcsque k tous les jours du passage de la grande 

 tache les photographies au spectroh^Iiographe, mais on n'a 

 oas obtenu autour de la tache des tr^s-grandes masses 

 faculaires. A. Riccd. 



Catania, October 10. 



