NOTES. 



ASTRONOMY. 



By A. C. D. Cro-M.melin, B.A., D.Sc, F.R.A.S. 



THE ORBIT OF DELTA ORIONIS— This star, the 

 right-hand member of the belt, lying alxnost exactly on the 

 celestial equator, is an interesting spectroscopic binary. 

 A discussion of its orbit, by Frank C. Jordan, appears in 

 " Publications of Allegheny Observatory'," Volume III, 

 part 15. He uses both his own and earlier photographs of 

 the spectrum, and thus has obser\-ations available extendiirg 

 over ten years. The spectrum is of Type Bl (helium type). 

 No secondary spectrum can be traced ; so evidently there is 

 great disparity' in the light-giving power of the components. 



The most probable value of the period is 5 -73257 days ; 

 the eccentricity, 0-09 ; the orbital velocity, 100 kilometres 

 per second ; longitude of periastron, 5° in 1902, 20° in 1910 ; 

 the recessional velocity,' of the centre of gravity, 23 kilo- 

 metres per second in 1902, 15 kilometres in 1910 ; a sin i 

 =7,850,000 Idlometres. 



Also, if »«i, in^ denote the masses of primar>' and second- 

 arj' stars (the Sun being unity), 



m.? sin^ i 



r^—. -,3 = 0-588. 



The change in the longitude of periastron is doubtful, 

 as there is considerable uncertaints' in the determination ; 

 it is, however, in accord with what tidal action would lead 

 us to expect. The change in the rate of recession of the 

 e.g. may only arise from the different personality of the 

 obser\'ers ; it may, on the other hand, indicate revolution 

 round a third member of the system, such as is beheved to 

 take place in the case of Algol. 



There are many spectroscopic binaries for which our 

 ignorance of the value of i is complete : this is not the case 

 with Delta Orionis, for Mr. Joel Stebbins found some years 

 ago, with the aid of his sensitive selenium photometer, 

 that it is an Algol variable, though the change of Ught is 

 too small to detect by ordinary methods. Hence we see 

 the system nearly edgewise, and a partial eclipse occurs in 

 each revolution. 



If we assume for the companion a mass half that of the 

 primary, and conjecture for the radii of the two one and 

 a half and one milUon kilometres, also taking the amount 

 echpsed as one-quarter of the diameter of the primary, 

 i comes out 86°. It is unnecessary to know it very accurately, 

 since the sine of an angle near 90° changes slowlj'. Under 

 these assumptions the masses come out 10|, 5s, that of 

 the Sun being 1. 



If we assume equal masses, and take i=83°, the mass of 

 each is two and a half times the Sun's. The total mass of 

 the system probably hes between ten and twenty' times the 

 Sun's. From the minuteness of the star's proper motion 

 it is beheved to be very distant ; hence the luminositv of 

 the primarj' is, presumably, very great in proportion to its 

 mass ; in other words, its density is small, and its radius 

 may not improbably be considerably greater than that 

 assumed above. This would diminish the value of sin ;, but 

 not enough to seriously affect the masses. 



This star is one of those in whose spectra the H and K 

 hnes of calcium do not share in the periodic displacement. 

 No ver\' satisfactory explanation of this peculiarity has 

 been arrived at, but it is supposed to indicate an extended 

 calcium cloud enveloping the system. Jlr. Jordan finds 

 18-5 kilometres per second as the velocity of this calcium 

 cloud away from the Sun. This is 3-5 kilometres greater 

 than the velocity of the e.g., but the difference is not large 

 enough to lay great stress upon. He notes that the Sun's 

 own speed is about eighteen kilometres per second away from 

 the star ; hence the calcium cloud is practically at rest 



with reference to the sidereal system — at least as regards 

 the radial component. This is in accord \rith the fact 

 that the stars of early spectral type have in general small 

 velocities. It will be of great interest to follow this star 

 fairly continuously, both with the spectroscope and photo- 

 meter, to ascertain whether the motion of the periascion 

 and change in the speed of the e.g. are verified. It is quite 

 likely that an analysis of the hght-curve during echpse 

 would give further information about the diameters, but 

 I have not at present access to the details. 



MOULTON AND CHAMBERLIN'S PLANETESI.MAL 

 HYPOTHESIS. — Mr. T. C. Chamberlin gives an interesting 

 exposition of this hypothesis in Scientia for October. The 

 theory does not deal with the birth of the Sun, which is 

 supposed to have formerly existed as a soUtary orb. Another 

 Sun is supposed to have passed fairlj' near it (according 

 to the authors, a distance of a hundred milhon miles, 

 or even more, would not be too great to produce the 

 effects they postulate : approaches within this distance 

 would be vastly more frequent than actual coUisions). 

 The result is tidal distortion of each star, protuberances 

 being raised on opposite sides of them. These are supposed 

 to have reached such a height that a large quantity of 

 matter on each side broke off from the parent star and 

 commenced to describe orbits round it, the moment of 

 momentum required for this revolution being derived from 

 the attraction of the other star. This acquirement of 

 extraneous moment of momentum is the leading motive 

 of the theory : " The Sun holds about seven hundred and 

 forty-five out of seven hundred and forty-six parts of the 

 total matter of the solar system, wliile it only carries about 

 two per cent, of its moment of momentum. This leads to 

 the conviction that a new agency came in, after the 

 original formation of the Sun, and gave to a very small 

 fraction of the solar matter, after it had been drawn out from 

 the Sun, a special endowment of momentum." The two 

 streams of matter would form a double spiral, of a form 

 that we meet with in numerous nebulae. The argument 

 from analogy is used by the authors to support their theory 

 Another argument, not used by them, seems to me to be the 

 constitution of meteors, which frequently contain a large 

 quantity- of hydrogen. This would be explained if they had 

 once formed part of the crust of the Sun, on the hypothesis 

 that this crust had already solidified before the approach 

 of the other Sun, but was then disrupted by tidal action. 



I shall continue this note next month. 



BOTANY. 



By Professor F. Cavers, D.Sc, F.L.S. 



EFFECTS OF ELECTRIC DISCHARGE ON PLANTS. 

 — Many experiments have been made during recent years 

 in which plants, otherwise under normal conditions, have 

 been subjected to an electric discharge from an overhead 

 system of wires during a considerable portion of their 

 growing period, and, as a result, acceleration of growth and 

 increase in yield have been invariably reported. Since 

 this treatment must considerably alter many factors in 

 the plant habitat, and in the plant's reaction to this habitat, 

 it is difficult to ascribe the effect, apparently due to the 

 electric discharge, to any particular physiological cause. 

 Priestley, who has taken a prominent part in this line of 

 investigation, records in a recent paper, in collaboration 

 wth Knight {Annals of Botany, Volume XXVIII), some of 

 the first attempts to analyse the efiect of the discharge 

 upon the plant by investigating under laboratory con- 

 ditions the effect produced by such discharge upon one 

 ph5'siological function, namely, respiration. Experiments 

 were made \\ith small direct currents at a relatively low 



51 



