400 



NA TURE 



[February 27, 1902 



from which the solitary worker shrinks, but which are, never- 

 theless, essential to the development of chemistry. Brilliant 

 discoveries might be made in them, but incidentally, and not 

 as their main purpose. 



The table of atomic weights issued annually by the inter- 

 national committee appears in the January number of the 

 Bcriihii, a.ni the table, bxsed upon oxygen = i6, is unaccom- 

 pnied by the didactic table with hydrogen=l. The with- 

 dr.iwal of the didactic table is in accordance with a widely 

 expressed wish. It is generally felt that if oxygen is to be 

 taken as l6 for any purpjss it should be taken as 16 for all 

 purposes. Discussing this subject in a paper recently contri- 

 buted to the .\merican Society of Sciences and Arts, I'rof. 

 Richards made a strong appeal 10 chemists to conform to the 

 decision of the international committee. He pointed out that 

 oxygen has actually served as the experimental standard of 

 reference in a great majority of cases, that the great bulk of 

 valuable work has already been published on the basis 

 oxygen = r6'ooo, and that the use of this standard involves no 

 important didactic difficulties. He contends that the decision 

 of the representatives of the international committee is in itself 

 an important reason for adopting this standard, and that 

 uniformity of u.sage is more important than any of the special 

 advantages claimed by either side in the discussion. The only 

 aherations of atomic weights in this year's table are of calcium 

 from 40 to 401, iron from 56 to 55'9, and tellurium from 127 

 to 127-6. 



The additions to the Zoological Society's Gardens during the 

 past week include two Guinea Baboons (Cynocephahts sphinx), 

 a Red-footed Ground Squirrel (Xerus erythropiis) from West 

 Africa, presented by Captain R. H. Wilford ; a Snow Leopard 

 {Felis iimia) from Northern India, presented by Captain H. 

 NichoU ; two Half-collared Turile Doves ( Tarlnr scmitonjtialus) 

 from West Africa, presented by Captain Thorne ; a Ring- 

 necked Pheasant (P/iasianiis torquatus) from China, presented 

 by Mr. B. Tufnell ; seven Black-headed Gulls {Lirtis ridi- 

 buiidus), a Common Gull (Larus cantts), European, presented 

 by Mr. E. J. W. Eldred ; a Green Monkey (Cercopithecus 

 callitriihus), an Erxleben's Monkey (Ceiiopitheais erxlebeiii), 

 eight West African iMve-MnA^iAgaportiis ptillaria) from West 

 Africa, a Greater Sulphur-crested Cockatoo (Cacaliia galerita) 

 from Australia, a Levaillant's Amazon {Chrysalis Imaillanti) 

 from Mexico, ten Common Toads (Bufo vulgaris), European, 

 a Loggerhead Turtle {Thalassochelys caretta) from Tropical 

 .Seas. 



OUR ASTRONOMICAL COLUMN. 

 Astronomical Occurrences in March. 

 .M.ir. 3. 22h. Vesta in conjunction with the moon. Vesta 

 "° 35' S. 



5. I5h. Saturn in conjunction with the moon. Saturn 



5- I' S. 



6. I4h. Jupiter in conjunction with the moon. lupiter 



5°4';S. 



7. 7h. \ enus in conjunction with the moon. Venus 



2° ir N. 

 12. loH. 12m. Minimum of Algol (/8 Persei). 

 15. 7h. im. Minimum of Algol (/3 Persei). 

 15. Venus. Illuminated portion of disc = O'igS, Mars 



= I 'COO. 

 17. 2h. om. Mercury at greatest elongation (27" 41' W.). 



17. 9h. 19m. to loh. i6m. Moon occults 26 Geminorum 



(mag. 5-1). 

 iS 5h. 4Sm. to 6h. 14m. Moon occults 68 Geminorum 

 (mag. 5-0). 



18. I5h. 19m. to iSh. 58m. Transit of Jupiter's Sat. III. 

 20. Sfi. 27m. to gh. 43m. Moon occults u Leonis 



(mag. 5-6). 

 20. igh. om. Venus at maximum brilliancy. 

 NO. 1687, VOL. 65] 



Mar. 21. ih. om. Sun enters Aries. Spring commences. 



21. Saturn. Outer minor axis of outer ring = 13 "'75. 



22. ilh. 19m. to I2h. 24m. Moon occults /■'• Leonis 



(mag. 5-5). 



28. I3h. 4ini. to I5h. om. Moon occults v Scorpii 



(mag. 4-5). 



29. I3h. Mars in conjunction with sun. 



OlISERVATIONS OF 900 DoUBI.E AND MflilllE STARS.— 

 The first of the astronomical series of publications from the Uni- 

 versity of Pennsylvania consists of the measures of 900 double 

 and multiple stars made by Prof. Doolittle with the iS-inch re- 

 fractor of the Flower Observatory. These observations were 

 made during the period 1897 January 1 and 1900 (Jctober 15. In 

 all cases a power of 592 diameters was employed. Twenty-two 

 of the stars are now catalogued for the first lime, having been 

 discovered during the observation of neighbouring doubles. 



The 18-inch objective is the largest lens made by Brashearup 

 to the present time, and has given every satisfaction, both as to 

 resolving and ligh'.-grasping power. The mounting, by Warner 

 and Swasey, is of similar construction to the Lick and Verkes 

 instruments {Puhlicatioiis of lite Universily of Pennsylvania, 

 Astronomical Series, vol. i. part iii.) 



Observations of 194 Double Stars. — Bulletin No. 11 

 from the Lick Observatory contains a list of observations made 

 by Mr. R. G. .-Miken during 1900 and 1901 with the 36-inch and 

 I2inch refractors. Many of the stars are difficult pairs, and in 

 most cases the 36inch telescope was employed, with powers 

 ranging from 1000-2400. 



RADIO-ACTIVITY AND THE ELECTRON 

 THEORY} 



T7 LECTRONS emanating from radio-active bodies behave 

 like material particle>, and are impeded by the molecules 

 of the surrounding medium, in contrast with ether waves, which 

 are not thus afi'ccted except by absorption. It is not difficult t'< 

 put these indications to test. A pair of shallow cells, A B 

 (Fig. I), I '5 mm. deep and 25 mm. square, were made by 

 cementing slips of glass to a thick glass plate. The cells were 

 fille<l to the same depth with a radio-active substance chiefly 

 containing actinium.'-' Over cell .\ was placed a piece of thick 

 lead pipe, 28 mm. high and 25 mm. internal diameter, to ensure 

 that any emanations from the active substance in \ would be 

 confined to the inside of the hollow cylinder. The radio-active 

 substance in \\ was freely exposed to the air, save for a pillar of 

 lead at c, to support the sensitive film. .\ sensitive film was 

 laid horizontally over the cylinder and support c. On the film 

 was a plate of glass, and cylinder and film were pressed together 

 by heavy weights. The whole was covered in a light-tight bo.x 

 and put in a dark cupboard. 



At the end of forty-eight hours the film was removed and 

 developed. There was a strong action shown over cell A (the 

 one covered by the lead cylinder), but over B, the cell exposed 

 to theair, there was no visible impression. Measured in Mr. 

 Chapman Jones's " Opacity Meter" ' the results were : — 

 Image over cylinder — Opacity log.' = 79; Opacity^ = 617. 



The experiment was repeated, using the same apparatus, 

 but a different pfeparation of actinium. In this case the ex- 

 posure was for seventy-two hours. As before, there was a 

 strong impression over cell A and none over cell B. The figures 

 were ; — 



Opacity log. = -89 ; Opacity = 771. 



The.se experiments indicate that the electrons from the radio- 

 active agent, chiefly actinium, partake of the properties of a fog 

 or mist of material particles, capable of diffusing away in the 

 free air like odoriferous particles, when not kept in by a thick 

 melal screen. 



A further experiment was now tried with the same apparatus, 

 the agent a strongly active radium and barium bromide. This 

 material being self-luminous, a sheet of black paper was placed 



1 Hy Sir Willi.im Crookts, F.R.S. i\ l>.-»per reaj before the Royal 

 Society on Februaiy 6. 



- Tile body 1 called Uranium X in my Royal Society paper, May 10, 

 1900, has since proved to be M. Ucbierne's Actinium. 



** The Photographic Journal, vol. XX. p. 86, December ?i, 1895. 



-> The opacity logarithm represents the density of the image, absolute 

 density being represented by 2*00. 



^ 1 he ''opacity" is the whole number corresponding to the "opacity 

 log." The "opacity" is directly proportional to the photographic energy 

 acting on the sensitive surface. . 



