172 



NATURE 



[August ii, 1910 



agree as to the nature of the Pwdre Ser, and I must say 

 that whenever I have observed its manner of occurrence 

 it has seemed to me to grow out of the sod — but I would 

 not like to say that what I have seen has always been the 

 same kind of matter. 



The very circumstantial account given by Morton, that 

 something of the kind is disgorged by birds, is confirmed 

 by other later observers. 



Although we must not too hastily accept what is un- 

 doubtedly a vera causa as the only explanation, we may 

 feel that we are movinig in the right direction to find the 

 answer to the question, What is it? 



The question why it is associated with falling stars has 

 received a plausible e.xplanation from Messrs. Grove and 

 Griffiths (Nature, July 21); but falling stars do not appear 

 to hit the ground so that an observer can walk up to the 

 spot where they seem to have fallen, as in the case of light- 

 ning or thunderbolts, and if we bring in possibilities of 

 other luminous bodies we raise the difficult question of 

 lambent fires, &c. The star-like radiating form of the 

 jelly-fish, like that of the star-fish, is sufficient to explain 

 the name given by Admiral Smyth (July 21, p. 73). 



While our botanical friends are finding out for us what 

 it is, may I hope that some of our literary friends will 

 trace the belief back further than the sixteenth century, 

 when we find it accepted as if founded upon well-known 

 facts? T. McKf.nny Hughes. 



July 29. 



The Blood sucking Conorhinus. 



It may. interest readers of Nature to be informed that 

 the great South American bug figured on p. 142 of the 

 issue of .August 4 punished Charles Darwin when travelling 

 in the Pampas, happily without infecting him with its 

 trypanosome (see "Journal of a Naturalist," ed. 1845, 

 P- 330). J. D. H. 



The Camp, near Sunningdale, August 5. 



[Subjoined is the description to which our correspondent 

 refers. — Ed. Nature.] 



".We slept in the village of Luxan, which is a small 

 place surrounded by gardens, and forms the most southern 

 cultivated district in the Province of Mendoza ; it is five 

 leagues south of the capital. At night I experienced an 

 attack (for it deserves no less a name) of the Benchuca, a 

 species of Reduvius, the great black bug of the Pampas. 

 It is most disgusting to feel soft, wingless insects about 

 an inch long crawling over one's body. Before sucking 

 they are quite thin, but afterwards they become round and 

 bloated with blood, and in this state are easily crushed. 

 One which I caught at Iqulque (for they are found in 

 Chile and Peru) was very empty. When placed on a 

 table, and though surrounded by people, if a finger was 

 presented the bold insect would immediately protrude its 

 sucker, make a charge, and, if allowed, draw blood. No 

 pain was caused by the wound. It was curious to watch 

 its body during ttie act of sucking, as in less than ten 

 minutes it changed from being as flat as a wafer to a 

 globular form. This one feast, for which the benchuca 

 was indebted to one of the oflicers, kept it fat during four 

 whole months ; but, after the first fortnight, it was quite 

 ready to have another suck." 



The Early History of Non-Euclidean Geometry. 



In a recent number of Nature (June 30) there appeared 

 a review of a book by G. Mannoury on the philosophy of 

 mathematics, and the reviewer emphasised a statement of 

 the author to the effect that the claim for Gauss that he 

 was the first to assert the possibility of a non-Euclidean 

 geometry is threatened by F. K. Schweikart, who in 

 December, 1818, sent a note to Gauss asserting the exist- 

 ence of a geometry in whjch the sum of the angles of :i 

 tri.ingle is less than two right angles. The facts about 

 Schweikart were made known fifteen years ago bv Stackel 

 ::nd Engel (" Theorie der Parallellinien," p. 243), and the 

 'irtual- documents were published in Gauss's " Werke," 

 Bd. viii. ■ (1900). It must be admitted that Schweikart 

 NO. 2128, VOL. 84] 



arrived independently at this result, though it is not 

 so obvious that he had forestalled the " giant mathe- 

 matician." Schw 'ikart states his hypothesis very clearly, 

 and explains that Euclidean geometry is a special case of 

 a more general geometry. On the other hand. Gauss was 

 interested in the theory of parallels from at least 1799; 

 and some time between 1808 and 1816 he arrived at the 

 belief that non-Euclidean geometry was possibly true, for 

 in 1808 he asserted that the idea of an a priori linear 

 constant (the " space-constant ") was absurd, while in 1816 

 he declared that, while seemingly paradoxical, this idea was 

 in no way self-contradictory, and that Euclid's geometry 

 might not be the true one. In his comments on 

 Schweikart 's note, he exhibits quite an extensive know- 

 ledge of non-Euclidean trigonometry. 



Of course, the development of non-Euclidean geometry 

 and trigonometry is due independently to Lobachevskij 

 (1829), and Bolyai (1832), and even that was worked out 

 to a large extent previously by Lambert (1786), and still 

 earlier by the Italian Jesuit Saccheri (1733), though neither 

 of these two conceived for a moment the possibility of non- 

 Euclidean geometry being true. 



It is interesting in this connection to recall the hesitancy 

 of Cayley to accept non-Euclidean geometry, although he 

 himself practically inaugurated a new epoch. He never 

 seemed quite to appreciate the subject, and on one occasion, 

 at least, fell into a mistake in writing about it. In his 

 article " On the Non-Euclidean Plane Geometry," Math. 

 Papers, vol. xiii., p. 237, he inadvertently takes the equa- 

 torial circle of the pseudosphere (the surface of revolution 

 of the tractrix) as representing the points at infinity, 

 whereas the absolute is only represented by a single point, 

 viz. the point at infinity on the pseudosphere. 



D. M. Y. S0MMERVII.LE. 



The University, St. Andrews, July 26. 



The Total Solar Eclipse of April 28, 191 1. 



Whilst astronomers who intend to observe this eclipse 

 .'ire choosing from amongst the Vavau, Tau, Nassau, and 

 Danger Islands, the best one on which to land, it may 

 be useful to state the totalities of- the eclipse in these 

 islands. 



From the calculation of the phases obtained by the 

 Besselian method, and with the data of the " American 

 Ephemeris," I have found the following values: — 



Totality = 3 ^66 



V.ivau (arch, rf Tonga) 

 Tau (arch, of Samoa) 

 Dangei (arch, of Union) ... 

 Nassau ( ,, ) ... 



The geographical coordinates of these islands, adopted 

 in the calculations, are respectively : — 



= 3 l?"* 

 = 4 9'9 



Mars in igog as seen at the Lowell Observatory. 



The accompanying prints are photographs of the globe 

 of Mars, representing the details seen on the planet at the 

 Lowell Observatory at the last opposition in 1909. 



These maps demonstrate strikingly the development of 

 the canals from the melting cap, shown by the number 

 of canals visible in the southern hemisphere at the time, 

 especially about the south pole, and by the absence of 

 canals in the northern one, notably in the neighbourhood 

 of the north polar cap. 



The canals numbered 659 or 660 are the two great new- 

 canals, of which the account has already been published, 

 and of which the size enabled the advent to be established 

 with certainty. Several other examples of fresh origina- 

 tion are to be seen on the charts, about which the evidence 

 i^ hardly less conclusive. 



The white patches at some distance from the south pole 



