84 



KNOWLEDGE. 



[May 1, 1898. 



the fore-paws is a purely adaptive one, there can be no 

 reasonable doubt ; but whether the identical structural 

 conformation of the molar teeth of the two animals 

 indicates any real genetic affinity, or is merely inherited 

 from an old ancestral type which may have been common 

 to many groups, is far less easy to answer. 



The marsupial mole, or ur-quamata, as it is termed by 

 the aborigines, inhabits a very limited area lying about a 

 thousand miles to the interior of Adelaide ; and even there 

 appears to be of extreme rarity. According to observations 

 supplied to its describer, Dr. E. C. Stirling, the creature 

 is generally found buried in the sand under tussocks of the 

 so-called porcupine-grass (Triodia), and its food appears to 

 consist of insects and larvie. The animals appear only to 

 move about during warm, moist weather ; and as they are 

 extremely susceptible to cold, it is probable that they lie 

 in a more or less torpid condition during the winter 

 months, when the surface of the gi'ound is often white with 

 frost. When on the move, the marsupial mole is said to 

 enter the sand obliquely, and to travel for a few feet or 

 yards beneath the surface, when it emerges, and after 

 traversing a short distance above ground, once more 

 descends. As it seldom tunnels at a depth of more than 

 two or three inches below the surface, its course may often 

 be detected by a slight cracking or movement of the 

 surface as the tunnel proceeds. Both in this respect, and 

 in the nature of its food, the ur-quamata therefore exhibits 

 a further analogy with the golden mole. In burrowing, 

 the leathery shield of the head is said to be brought into 

 play as a borer in the soft sand. 



As regards the advantages obtained by the mammals 

 which have taken to a burrowing subterranean existence, 

 it will be manifest that these are twofold. In the first 

 place the creatures are secure from all foes, except those 

 which, like the weasel and the snake, are able to follow 

 them into their underground labyrinths ; while, secondly, 

 they tap a food-supply (whether animal or vegetable) which 

 is inaccessible to most other animals. In the case of the 

 mole at least, whose habitations are generally made in 

 comparatively hard ground, the life must be an incessant 

 round of labour ; and to our thinking, at any rate, the 

 existence of all these burrowing creatures must be so dull 

 and monotonous as to leave no question as to whether it 

 is worth living. 



STELLAR SPECTRA AND STELLAR 

 VELOCITIES. 



By Miss A. M. Cleeke, Authoress of " The System of the 



Stars" and "A Popular History of Astronomy diiriny the 



Nineteenth Century," dr., dr. 



THE first spectroscopic review of the heavens, begun 

 by Father Secchi at Kome in 1863, showed pretty 

 clearly that the geometrical and physical relations 

 of the stars are, to some extent, interdependent ;* 

 but the establishment of any general connection 

 of the sort was only rendered possible by the publication 

 of the Draper Cataloyue. Not that the data provided in 

 this repertory — valuable and ample though it lie — are well 

 enough assured to serve as the basis of other than pre- 

 liminary conclusions. For the method by which they were 

 obtained might be called without disparagement a rough- 

 and-ready one ; it was applied too extensively to be applied 

 with discrimination. The stars had to be taken in batches 

 as they came, with an unvarying exposure of five minutes, 



• Report, British Association, 1868, p. 169. 



which was necessarily too long for some, and too short for 

 others. The results should, then, be accepted most thank- 

 fully, and with full recognition of the energy, ingenuity, 

 and resourcefulness employed in procuring them ; but 

 they should be accepted for what they are worth, and no 

 more. 



Again, the absence of settled criteria of classification 

 gives rise to uneasy reflections. It is impossible not to 

 feel some distrust of a system which recognizes no spectro- 

 scopic distinction between Capella and Kigel, both being 

 comprised within the sub-class F ; and indeed most of 

 the stars designated in the Draper Catnloyiie as of the 

 " Capellan " variety — sub-classes F and G — rank visually, 

 according to Vogel, as of the Sirian type. How then, we 

 cannot but ask ourselves, are differences so numerous and 

 so glaring to be reconciled ? To what court of appeal can 

 we turn when eye and camera disagree ? Decisions, more- 

 over, presuppose definitions ; and no agreement has yet 

 been come to as to what constitutes the essential distinction 

 between a first and a second type star. Perhaps the best 

 available resides in the relative strength of the K-line ; 

 and as it lies in the faint violet region of the specti'um, its 

 adoption would devolve the task of their discrimination'' 

 upon photography. Thus the Dr(tper Cataloyue, in the 

 construction of which this test has been carefully, though 

 not exclusively, regarded, may turn out to be the best 

 extant authority in the matter. The ratification of its 

 data would be the more welcome as it would tend to fortify 

 the important conclusions drawn from their discussion, 

 some of which have been adverted to in the last number 

 of Knowledgk. 



The most fundamental of these relates to the proper 

 motions of the different orders of stars. Members of the 

 solar class, whether of the Capellan or the Arcturian 

 species, traverse the sphere much more rapidly than 

 " white stars " resembling either Vega or Kigel. This 

 seems to be a particularly solid fact. The chances are 

 small that it will be overthrown by the progress of research. 

 It is, then, of great interest to investigate its true meaning. 

 What are we to understand by it '? Are the less mobile 

 stars, on the average, more distant, or are they animated 

 by a lower real speed '? If proper motion may be taken to 

 be in any way a test of remoteness, the former alternative 

 must be adopted ; yet, as Mr. Eanyard truly remarks, 

 " the assumption is by no means self-evident that all types 

 of stars are moving with the same average velocity." 

 Certainly not. The proposition requirss to be proved ; 

 and if the evidence alleged in its support be inconclusive, 

 all deductions regarding spectral distribution, in which 

 mean proper motion is accepted as a measure of mean 

 distance, must be accounted vitiated by a fundamental 

 vmcertainty. It seemed, then, worth while to recur to the 

 subject for the purpose of enabling the readers of Know- 

 ledge to judge for themselves how far Prof. Kapteyn had 

 succeeded in proving a general equality in actual physical 

 speed between the constituents of the two chief stellar 

 orders. 



The principle of the inquiry was explained in the April 

 number of Knowledge. It is that the component of stellar 

 motion directed along a great circle passing through the 

 sun's apex affords, since it is of perspective origin, a safe 

 criterion of the distance from the advancing solar system 

 of the group of stars to which it belongs. Either the 

 remaining portion of their apparent displacements, on the 

 other hand, being that directed across the line of the sun's 

 way (designated t), or the sum total of their movements 

 (/a), affords an index to their genuine and original rate of 

 transport. Evidently, then, when the perspective element 

 and the original element in the proper motions of two 



