January 31, 19 18] 



NATURE 



425 



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 with 

 the writers of, rejected manuscripts intended for 

 this or any other part of Nature. No notice is 

 taken of anonymous communications.] 



The East and West Asymmetry of Solar Prominences. 



It has attracted the attention of astronomers for 

 ^ome time that solar prominences appear to be more 

 numerous on the east, or advancing, side of the sun 

 than on the west, or receding, side, and systematic 

 observations have been instituted to test this unexpected 

 result. The current Kodaikanal Bulletin (Ivii., August, 

 1917) seems to establish it definitely by a very com- 

 plete analysis of the observations for the first half of 

 1917. Of prominences projected on the solar disc as 

 absorption markings, 529 per cent, as regards area, and 

 534 per cent, as regards number, were on the eastern 

 side of the central meridian. Of reversals and dis- 

 placements (largely preponderant towards the red) of 

 hydrogen lines on the disc, there was a like excess on 

 ihe eastern side. But of the bright prominences 

 directly observed on the limb there was no excess as 

 regards number, and only a slight excess as regards 

 iirear. 



The solar disturbances must presumably be uniformly 

 <iistributed all round the sun's equator; it would seem 

 to be extremely unlikely, as is generally recognised, 

 that the side which happens to be presented to the earth 

 or any other planet should exhibit special features. But 

 it has doubtless not been overlooked that a more prob- 

 ;ible mode of explanation is open. Although the char- 

 acter of the prominences can scarcely be affected b}' 

 any influence of the earth, yet their appeiirance may 

 be considerably affected by their own configuration 

 with respect to the line of sight of the observer. The 

 outer regions of the solar atmosphere are rotating more 

 rapidly than the parts below; if then a prominence 

 pushed up from below into the atmosphere sloped for- 

 wards in the direction of the sun's rotation instead of 

 Ijcing on the average perpendicular to the surface, it 

 would present a different aspect and different depth 

 in the line of sight to the obsejrver, according as it is 

 on the advancing or receding side of the sun. The 

 darkness of the absorption markings on the disc would 

 depend on the depth of material through which the light 

 had to penetrate to the observer, and perhaps also in 

 consequence the number of shadings that would be 

 counted as markings would be affected. The amount 

 and direction of this influence it may be hazardous to 

 guess at, but it might just be possible to detect some 

 slight difference in the general appearance of the mark- 

 ings east and west. To the bright prominences on the 

 limb these considerations would apply in a smaller 

 degree, if at all. J. I- 



Cambridge, January 26. 



Carnotite Ores and the Supply of Radium. 



In Nature for October 25, 19 17, there appeared a 

 review of Dr. P. E. Browning's book, " Introduction 

 to the Rarer Elements." A special chapter devoted to 

 I he radio-elements was contributed by me, and in com- 

 menting on this section the reviewer takes exception to 

 a statement that " the chief source of radium has been 

 the minerals containing a higher proportion of 

 uranium, principally carnotite, and the present supply 

 has been largely obtained from the carnotite ores of 

 south-western Colorado." Since the comments of the 

 reviewer suggest the possibility of an even more wide- 

 spread misconception of the true conditions, I am 



NO. 2518, VOL. 100] 



taking the liberty of mentioning some of the facts 

 upon which the above statement is based. 



The minerals containing a higher proportion of 

 uranium are the several varieties of uraninite (includ- 

 ing pitchblende, cleveite, thorianite, etc.), autunite, 

 carnotite, gummite, uranophane, and a number of 

 others which occur only in comparatively small quan- 

 '' tities. The ores of uranium from which the supply of 

 i radium in commerce has been obtained consist of mix- 

 tures of relatively small proportions of the.se minerals 

 with large proportions of valueless mineral matter, 

 chiefly silica. Thus in the carnotite ores from Colorado 

 the uranium mineral constituent is carnotite containing 

 sometimes as much as 55 per cent, of uranium, while 

 ; the actual content of uranium in the ore is in most 

 i cases scarcely more than 2 per cent. Carefully selected 

 ! specimens of pitchblende from St. Joachimsthal may 

 I occasionally run as high as 70 per cent, uranium, but 

 the ores from this mine, even after concentration, 

 I seldom contain more than about 10 per cent, of 

 j uranium. Although no trustworthy information on 

 this topic has ever, to my knowledge, been made public, 

 I am strongly inclined to the opinion that the average 

 Cornwall ores (containing pitchblende as the chief 

 uranium mineral constituent) seldom contain more than 

 5 per cent, of uranium, and I have direct knowledge 

 that some shipments from this locality have fallen con- 

 siderably below this figure. Other examples might ba 

 given, but the above will suffice to justify the state- 

 ment that "the chief source of radium has been the 

 minerals containing a higher proportion of uranium." 

 It is clear that the uranium content of the ore is 

 seldom indicative of the proportion of uranium con- 

 tained in the uranium mineral which carries the 

 radium. 



In regard to the proportion of the world's supply of 

 radium salts contributed by the Colorado carnotite ores, 

 I may perhaps state that the greater proportion of the 

 radium salts furnished during the years 1903-12 by the 

 De Haen Company, of Hanover, and the Brunswick 

 Quinine Factory was extracted from these ores. The 

 chief source of the radium prepared by the Armet de 

 Lisle and other French factories has been the Colorado 

 ores, and large shipments have also been made to Great 

 Britain from this country. The National Radium In- 

 stitute and the Standard Chemical Company have 

 separated relatively large amounts of radium salts 

 from the Colorado carnotite ores exclusively. It has 

 been conservatively estimated by those familiar wit^h 

 the subject that prior to 1913 at least one-half of the 

 world's supplv of radium salts had been extracted from 

 Colorado carnotite, and the proportion supplied by the 

 Colorado ores since that year has been very much 

 larger. Additional information can be obtained by 

 those who desire it from the publications of the U.S. 

 Bureau of Mines (nut Bureau of Standards), the special 

 papers of Dr. C. L. Parsons, chief of the Division of 

 Mineral Technology, U.S. Bureau of Mines, and the 

 records of the "Hearing on Radium" before the U.S. 

 Senate and House of Representatives (Public Docu-' 

 ments, S. 4405, ahd H. J. Res. 185 and 186). 



Bertram B. Bolt wood. 

 Yale University, New Haven, Conn., U.S.A., 

 November 30. 



I AM afraid that Prof. Boltwood does not quite see 

 the reason whv I hesitated to endorse the statement 

 in question : it was necessary to quote the whole para- 

 graph as it appears in the' article, but my difficulty 

 I was confined to the words "principally carnotite." It 

 ' is, of course, obvious that the chief source of radium 

 I is' the minerals containing a higher percentage of 

 uranium, and it was for that reason only that I hesi- 



