192 



KNOWLEDGE. 



[October 2, 1893. 



Aerial mechanisms are capable of very much greater 



speed. Canon Tristram told the biological section of the 



British Association in his address — which, through his 



unfortunate illness, was read by Sir William Flower — that 



Herr Giitkc holds that godwits and plovers can do their 



240 miles an hour, and the spine-tailed swift, according to 



Dr. Jerdon, can breakfast in Ceylon and sup in the 



Himalayas on the same daj-. 



— I » t — 



A vei-y interesting topic, which is winning its way to 

 attention, is the periodic and secular vai-iation of the 

 latitude of places on the earth's surface. Prof, Chandler 

 has been laboriously investigating these movements for 

 some time. He has examined records extending over the 

 last half century, and including 33,000 observations of 

 latitude, and has come to the conclusion that the observed 

 value of latitude is the resultant arising from the super- 

 position of two periodic fluctuations. These are — (a) one 

 of 427 days due to a separation of the axis of rotation from 

 the chief axis of inertia, and (u) an annual one due to the 

 periodic shifting of the earth's centre of gravity in con- 

 nection with seasonal redistributions of moisture. 



Herr Alfred Mciller has been conducting a series of 



observations at Blumenan, upon the economy of those 



leaf-cutting ants described in "The Naturalist in Nicaragua," 



and he finds that they not only cultivate fungi, but also 



that they have by judicious selection evolved a specially 



suitable variety, with peculiar swollen lateral branches. 



The fungus garden is an enclosure, protected of course 



from the light, and thither the strips of leaf are taken, 



and crushed up by the jaws of the ants, to supply their 



crop with organic food. So efficient is the weeding out of 



unsuitable material by these little horticulturists, that 



some of the earth of the garden, grown in a nutritive 



solution, gave a perfectly pure culture, free even from 



bacteria. The ants appear to subsist entirely on their 



specialized fungus knol)?. 



— — ^-^-t — 



The Kev. .J. Mathew has been studying various Aus- 

 tralian rock and cave drawings. Many of these, it has 

 long been known, are of a character far above the 

 possibilities of existing aboriginal work, and indicative of 

 an altogether higher level of civilization in the artists. 

 One he describes is in red, blue, yellow, black, and white, 

 and represents a figure dressed in a long robe and with 

 the head surrounded by a kind of many-coloured halo. 

 Mr. Mathew has found on one such halo certain marks 

 which he interprets as the name of the chief god of 

 Sumatra, and he also finds many other facts, the frequent 

 presence of a sacred crocodile for example, which incline 

 him to give these interesting markings a Sumatran origin. 

 The natives can tell nothing about them, simply regarding 

 them as bogies. He thinks, however, the crude religious 

 notions of the aborigines may have been derived from 

 the forgotten predecessors of the Anglo-Saxon colonist, to 

 whom he ascribes these drawings. 



Erttrrs. 



[The Editor does not hold himself responsible for the opinionn or 

 statements of correspondents.] 



• 



To the Editor of K.nowledge. 



THE SUX AS A BRKiJIT-I-lXK .STAR. 



Dear Sir., — I have been greatly interested in reading 



Miss Gierke's valuable and suggestive paper on " The Sun 



as a Bright-line Star," and the discussion to which it has 



given rise in the August and September numbers of 

 Knowledge. May I be allowed, however, to point out 

 that an important matter seems to have been overlooked 

 by those who have taken part in the discussion. I refer 

 to the (hmhlc reverxiil of the H and K lines of the faculie. 

 A positive enlargement from a photograph taken at the 

 Kenwood Observatory is sent herewith to the Editor. It 

 clearly shows the bright H and K lines, with a central 

 dark line, not only in a facula, but also on the disc as far 

 as the slit extended. We here have e\idencc that a large 

 area of the sun's surface was uniformly covered with a 

 layer of calcium vapour hotter than the photosphere below 

 it, and this again was capped by cooler calcium vapour 

 which exercised sufficient absorptive power to cause a dark 

 line to appear in the centre of the bright line originating 

 in the hotter la3'er. Instances of double reversals of H 

 and K extending without interruption for great distances 

 are very common. Sometimes the lines can be traced 

 entirely across the solar disc. The two bright components 

 of the doubly-reversed lines are about equal in width to 

 the central dark component. In certain cases portions of 

 one of the bright components seem to be missing, while 

 the other bright component is unbroken. Where the slit 

 lies across a facula the two bright components widen and 

 increase in brilliancy. Their form is then spindle-shaped, 

 and the central dark line has become fainter and narrower. 

 The accompanying photograph perfectly illustrates this 

 point. Two causes may be involved in bringing this about. 

 In the first place the increased thickness of the radiating 

 calcium vapour (assuming a facula to be an elevation in 

 the photospherio calcium stratum) tends to increase the 

 brightness of the lines and also to widen them, on account 

 of the increased radiation on both sides of the centres of 

 maximum brilliancy. Again, if we assume the cooler 

 calcium to overlie the hot calcium in a layer of uniform 

 depth (a depth "necessarily greater than the height of the 

 facuhc), then the absorption should be least in the faculne, 

 where the overlying stratum of cool vapour is thinnest.* 

 I am inclined to think that the actual appearance of the 

 lines is such as to indicate the simultaneous existence of 

 both these conditions. 



Now let us consider the case of Mira Ceti. Suppose the 

 thickness of the layer of cool calcium to be increased to 

 such an extent that not only the centre but the whole of 

 the bright line is blotted out. This might occur even if 

 the H and K radiations of the faculie were abnormally 

 bright. In the sun it is extremely uncommon for the 

 more refrangible hydrogen lines to be radiated by facuhr. 

 Nevertheless, it is not diflicult to imagine condition? 

 favourable to tliis result. Under these circumstances, if 

 there were insufficient cool hydrogen ii: the atmosphere of 

 Mira to absorb the radiations of the lower regions, we 

 should have a spectrum showing H and K broad and dark, 

 and the series of hydrogen lines bright, with the exception 

 of that near H, where the absorption of the calcium would 

 have blotted it out. 



Miss Gierke's explanation of the absence of the hydrogen 

 H line in Mira, therefore, seems to me a plausible one. 

 But the apparent similarity between this star and the sun 

 appears to be increased rather than diminished by such a 

 conclusion. Spectroscopists would do well to heed Miss 

 Gierke's suggestion as to the collection of further data for 

 the elucidation of this important subject. 



Very truly yours, 



GEORtiE E. Hale. 



* .Slioiild these ideas be confirmed by the results of future invcsti- 

 jj;ati()n, it might beeome possibh^ to roughly estimate the height of a 

 liu-iilu l)\ the eharaeti'r ol' the double reversal of the II uv K line in il. 



