April 8, 1920] 



NATURE 



Our Astronomical Column. 



Capella.— A knowledge of the parallax of Capella 

 is of special interest owing to the close resemblance 

 of this star's spectrum to that of the sun and the fact 

 that it is a spectroscopic binary with a period of 

 io4i days. Prof. F. Schlesinger and Mr. Z. Daniel 

 have made a new determination at the Allegheny 

 Observatory {Asir. Journ., No. 765). ITiey observed 

 both the principal star and Furuhjelm's distant com- 

 panion. The weighted mean parallax (absolute) is 

 oo68"±o-oo6". Earlier results are: Elkin, 0-079"; 

 Jost, 0051"; and Adams and Joy, o-ios''. 



The star B.D. + 6i° 2068, the proper motion of which 

 is 077", was also measured for parallax at Allegheny, 

 the large value 0-139" ±0007" (absolute) being found. 

 The corresponding absolute magnitude is 9-3 visual 

 and 10-5 photographic. 



Attempts were made some twenty years ago to 

 detect the duplicitv of Capella telescopically. It was 

 considered for a time that the 28-in. equatorial at 

 Greenwich gave an elongated image, but, in view of 

 the failure of the great American refractors, little 

 reliance was placed on this. A letter from Prof. Hale 

 dated January 6 last {Observatory, March) announces 

 that success has been obtained by interferometer 

 methods with the loo-in. reflector. It was deduced 

 that the separation on December 30, 1919, was 0042", 

 and the position angle 148° or 328°. It is hoped that 

 a continued series of such observations will give a 

 determination of the inclination of the orbit, and 

 hence of the masses of the components. There is 

 even a prospect that the diameters of such giant 

 stars as Sirius, Antares, and Betelgeux may be deter- 

 minable with the interferometer. 



Cape Observations of the Sun, Mercury, and 

 Venus. — The Cape observations of these bodies, made 

 with the new transit circle and the travelling-wire 

 micrometer during the five years 1907-11, have just 

 been distributed, together with a discussion of results. 

 The corrections to the equinox derived from the three 

 bodies are in good accord, and indicate that New- 

 comb's system of right ascensions needs the constant 

 correction —005s. The corrections to Newcomb's 

 longitudes of perihelia of Mercury, Venus, and the 

 earth are -0-78", +6-8", and -7-4" respectively. 

 These are of interest in relation to the Einstein con- 

 troversv. Newcomb applied the corrections to the 

 centennial motion of the perihelia given by the 

 Asaph Hall hypothesis, according to which gravita- 



tion varies as r-=-'"""'°°'"'. This formula gives 

 -I- 43-37", +16-98", and +10-45" for Mercury, Venus, 

 and the earth, whereas Einstein's formula gives 

 + 42-0", +8-6". and +3-8". It will be seen that the 

 .idoption of Einstein's law of gravitation bv the 

 Nautical Almanac would mean a movement towards 

 Newton's law, not a departure from it. 



The following semi-diameters of Mercury and Venus 

 at distance unity were deduced from the observa- 

 tions: — Mercury (latitude observations) 3-36" ±0-03", 

 (longitude) 3-79" ±0-17" ; Venus (latitude) 8-67"±o-03", 

 (longitude) 8-07" ±0-04". The tabular value's are 

 3-34" and 8-40". As these depend to a considerable 

 extent on observations made during transits, they 

 are likely to be somewhat too small. 



The Cape results may be too large owing to irradia- 

 tion, but, since all the observations were made in 

 davlight, this is not likely to be excessive. But as the 

 mass of Venus is onlv five-sixths that of the earth, 

 it is probable that its diameter is also smaller, whereas 

 the Cape figures make it equal to the earth. 



NO. 2632, VOL. 105] 



Basic Slag and its Uses in Agriculture. 



AN important discussion on basic slag and its uses 

 in agriculture, organised by the Faraday Society, 

 at which a number of leading representatives of the 

 steel makers and of agriculturists were present, was 

 held in the rooms of the Chemical Society on 

 March 23. Prof. F. G. Donnan presided over the 

 meeting. 



The discussion was opened by Dr. E. J. Russell, 

 who gave a general survey of the subject and indi- 

 cated the nature of the problems concerned. The basic 

 slag produced by the basic Bessemer process had 

 earned a high reputation as a potent agent in the 

 improvement of poor pastures. The effect is indirect, 

 and results from a stimulation of the white clover — 

 whether the action of the phosphate is on the clover 

 plant or on the nodule organism is not yet certain. 

 But whatever the reason, the effect on pasture land 

 is very marked, and British agriculturists could absorb 

 some 300,000 or 400,000 tons a year if this could be 

 produced. Unfortunately for agriculturists, however, 

 the Bessemer process is in danger of supersession, and 

 the basic open-hearth process is taking its place. This 

 new process gives two kinds of slag, both poorer than 

 the Bessemer slag in phosphates. 



One of these slags is made by the use of calcium 

 fluoride, and in consequence is less soluble than the 

 other. The great problem before the investigator at 

 the present time is to enrich the low-grade slags so 

 as to make them better worth grinding and transport 

 than they now are. 



Open-hearth slag made without fluorspar has 

 hitherto proved practically as effective as the old 

 Bessemer slag when compared on the basis of equal 

 amounts of phosphorus. Fluorspar slag has proved to 

 be of less value, although considerably better than 

 was at first thought. 



It is usually assumed, though by no means proved, 

 that the phosphate is the only effective constituent in 

 the slag. At various times it has been suggested that 

 lime, manganese, or iron might be useful; it is also 

 possible that slag contains a silico-phosphate which 

 might have more value than the ordinary phosphate. 



The enrichment of the slag cannot apparently be 

 brought about by any change in the pig iron, owing 

 to the great disparity in price between steel and slag ; 

 fractionation is, however, possible, or the addition of 

 ground mineral phosphate to the molten slag. Further 

 experiments would be necessary before any decision 

 can be made. 



Sir Thomas Middleton gave an account of the place 

 of basic slag in the agricultural system of this country. 

 British farmers tend more and more to produce animal 

 rather than human food. The two main human food- 

 crops — wheat and potatoes — occupied no more than 

 3,000,000 acres before the war, while 36,000,000 acres 

 were devoted to the crop requirements of cattle and 

 sheep. The value of the wheat and potatoes was 

 about 27,000,000^, while the live stock brought in 

 some 125,000,000^ The supreme importance of basic 

 slag arises from the fact that it helps to produce 

 animal food ; it is essentially a pasture fertiliser. In 

 the Cockle Park experiments the untreated pasture 

 yielded about 20 lb. of lean meat f>er acre per annum ; 

 after treatment with basic slag the yield rose to 105 lb. 

 of meat per acre. The results of many other experi- 

 ments show that on thousands of acres in this countr\' 

 the yield of meat might be increased by the use of 

 basic slag. Nor are the advantages of slag confined 

 to grass land. By ploughing up more grass, valuable 

 additions could be made to the tillage land, and if the 

 remaining grass were treated with basic slag there 



