April 22, 1886] 



NA TURE 



585 



can tell, be as copious as those of Sirius or Vega. But 

 they are intercepted in a deeply-laden atmosphere, which 

 can indeed be escaped by only a small per-centage of 

 their entire radiations. This explains at once the uniform 

 inconspicuousness of such objects. A star of this class 

 should possess, say, a hundred times the radiating surface 

 of Vega, to send us, from an equal distance, the same 

 quantity of light. 



No star of those yet known to show banded spectra of 

 either kind has an ascertained parallax. This is not 

 wonderful, since the stars at measured, or perhaps 

 measurable, distances from the earth, constitute a scarcely 

 perceptible fraction of the whole. Still, the fact remains 

 that all members of the two classes under consideration 

 are indefinitely remote. We are accordingly without the 

 means of estimating, even in the most general way, the 

 real quantities of matter contained in, or of light emitted 

 by, them. We can only say that their dimensions must be 

 very great in proportion to their apparent magnitudes. 



The question of their distribution is of much interest, 

 as involving their relations to the vast ground-plan of 

 the sidereal system. And one circumstance connected 

 with it becomes immediately evident. This is, their 

 largely predominant occurrence in and near the plane of 

 the Milky Way. M. Duner, it is true, considers that they 

 merely obey the general law of stellar condensation. 

 But this law applies more and more closely to the lessen- 

 ing orders of stars ; and we have just seen that, physically, 

 stars characterised by strong absorption should rank with 

 stars optically by many degrees their superiors. The 

 hypothesis, then, of some special connexion with the 

 galactic streams and rugosities is by no means excluded ; 

 and it is countenanced by statistics as to the distribution 

 of red stars in the southern hemisphere, recently afforded 

 by M. Pechiile (" Expedition danoise pour I'Observation 

 du Passage de V^nus," 1882, p. 38). 



One of the most assured peculiarities of stars with 

 banded spectra is their marked tendency to fluctuations 

 of light. Amongst innumerable examples of this con- 

 nexion may be cited "Mira" Ceti, and Gore's "new 

 star" in Orion, both of which display brilliant prismatic 

 flutings. Nearly all variables, in fact, save the few 

 which complete their cycle of change in a few days, 

 belong to one or other of the subdivisions of Class 

 III. Whatever may be the secret of their consti- 

 tution, it is indissolubly bound up with the still 

 mysterious cause of stellar variability. We can scarcely 

 penetrate the one without divining the other. Already 

 something is gained by the mere fact of the connexion 

 being established. We learn from it that the steadfast 

 shining of a sun or star is conditioned by the quality of 

 its surrounding gaseous envelope. Continuous study, 

 then, of the spectra of variables aflbrds probably the best 

 chance of progress in knowledge of their nature. M. 

 Duncr's incidental observations show that the reinforce- 

 ment and extension of banded absorption apparent at 

 minima, do not sufficiently explain the diminution of 

 light, which must accordingly be in part due, either to a 

 real failure of emissive power, or to an increase of general 

 absorption. The analogy of sun-spots favours the latter 

 alternative. 



JVI. Dundr concludes his valuable memoir with the ad- 

 mission that the order of stellar development postulated 

 by Vogel, and advocated by himself, may, after all, be the 

 inverse of that pursued in nature, — a possibility surely 

 worth thinking about. 



The heavens are no longer in our eyes " incorruptible." 

 Reason and revelation alike lead us to seek for symptoms 

 of growth and decrepitude in their bright inmates. Not 

 in human affairs alone " the old order changeth, yielding 

 place to new." But the subject is one on which we are 

 without the guidance of experience, and can scarcely 

 hope to acquire any, regard being had to the almost 

 infinite disproportion between our hurried notions of time, 



and the unimaginable leisureliness of cosmical progres 

 sion. Caution is then all the more needful, if we would 

 avoid wide wandering from the trutb. 



Now it has to be objected to Vogel's scheme, that it 

 gives no account whatever of suns in process of becoming. 

 Yet they must be as numerous, one would think, as suns 

 in process of decay. From the summit of brilliancy and 

 vigour, the course of decline is traced downward towards 

 the final quenching. But what of the other branch of 

 the curve ? Stars now at their acme of splendour must 

 have passed through long periods of preparation. Sirius 

 and Canopus, we are fully assured, did not all at once 

 blaze out in their present radiance. What, then, we 

 cannot abstain from asking, was their anterior condition ? 

 What quality of light did they emit ? How were their 

 atmospheres constituted ? What kind of spectra, in short, 

 would they then have afforded ? A system of classifica- 

 tion, based on the supposed order of stellar development, 

 in which no account is taken of this wide branch of the 

 inquiry, must be regarded as essentially incomplete. 



A. M. Clerke 



THE INSTITUTION OF NAVAL ARCHITECTS 



THE twenty-seventh annual session of the Institution 

 of Naval Architects, held at the rooms of the 

 Society of Arts, was one of the most successful of the 

 series. The meetings began on the 14th inst. and con- 

 cluded on the 17th. There were seven sittings, averaging 

 from three to four hours each, and no less than eighteen 

 papers were read and discussed. As on previous occa- 

 sions, too much was attempted to be done in the time 

 available, with the result that some important matters 

 received scant notice. This may be to some extent in- 

 evitable in a Society embracing such wide and varied 

 interests, yet meeting but once a year. But it may be 

 anticipated that the autumn meetings in the outports 

 which are now contemplated may somewhat relieve the 

 congestion in future. 



Lord Ravensworth presided as usual, and delivered a 

 Presidential Address, in which various matters of interest 

 were touched upon, inter alia the use of liquid fuel in- 

 stead of coal in steamships, the development of triple- 

 expansion engines, the prospects of shipping and the 

 statistics of shipbuilding, including the extended use of 

 steel. It may be hoped, although the immediate future 

 scarcely justifies the expectation, that before the next 

 meetings a change in circumstances may enable the 

 President to speak more cheeringly. On the other hand, 

 it is an undoubted fact that the period of depression 

 through which the country is now passing is forcing into 

 prominence inquiries into possible economies in the con- 

 struction and propulsion of ships which might otherwise 

 have been neglected. 



No less than seven of the papers read had relation to 

 the propulsion of steamships. The first on the list — " On 

 the Speed Trials of Recent War-Ships" — was I'ead by 

 Mr. W. H. White, Director of Naval Construction. It 

 contained a succinct account of the remarkable advances 

 made during the last quarter of a century in the speeds 

 and propelling machinery of war-ships. The fact that 

 huge battle-ships carrying enormous weights of armour 

 and guns are now driven at speeds of 17 to 18 knots — 

 20 to 21 miles per hour — is sufficiently remarkable. Yet 

 the fact that such a ship, weighing 10,000 tons, can be 

 driven 9 knots in an hour with an expenditure of only 

 I ton of coal is no less striking. Much has been learnt, 

 too, of late years as regards the influence of form upon 

 the resistances of ships ; thanks, in great measure, to the 

 researches of the late iVIr. Froude, whose work received 

 the substantial support of the Admiralty. In the paper 

 above mentioned it was shown that by suitable selection 

 of form, the Howe, a vessel of 9600 tons, 325 feet long 

 and 68 feet broad, was driven as easily as the Warrior 



