234 



KNOWLEDGE. 



[OCTOBEB, 1901. 



an automatic cut-off has now been added. This in- 

 genious niethwl should prove a gi'eat boon to animal 

 jihotographers, and will be an immense aid in securing 

 photogiaphs of very shy animals and birds. 



Breeding Rahits of the Swift (Zoologist, August, 1901. jip. 

 286-289).— By counting the birds in a. mhmy and examining 

 till- nests the Rev. F. C. R. Jourdain shows that one pair of 

 swiits will sometimes produce three eggs. Ahhougli three eggs 

 have often been found in one nest the third egg has generally 

 being considered tlie product of a second hen. If Jlr. Jourdain 

 has managed to accurately count the birds in the colony — a 

 .somewhat difficult task — then his c<i.se seems conclusively proved. 



Lesser White-Fronted Goose in Norfolk (Zoologist, August, 

 1901, p. 317). — Mr. F. C'oburn records that an adult female 

 of this bird, which is considered by many systematists t<i be 

 merelv a form of the white-fronte'd goose, was obtained in 

 Xoifolk on Januai-y 24th, 1900. 



All contributions to the column, cither in the way of notes 

 or photographs, should be forwarded to Habry F. Witherby, 

 at 10, St. Gcrminis Place, Blackheath, Kent. 



Astronomical.— Photographs taken by MM. Flam- 

 marion and Antoniadi, on August 19th and 20th, showed 

 that Nova Persei was surrounded by a nebulous aureola 

 having a definite sharp outline. 



Among recent publications relating to variable stars, a 

 |)aper by Dr. A. AV. Roberts, the well-known South African 

 observer, is of special interest. It is concluded that the 

 variable R R Puppis consists of two Ijodies, one being 

 three times the diameter of the other, but the smaller 

 being about twice as bright as the larger, and the distance 

 between their boundaries about two-thirds the radius of 

 the orbit. In the case of V Puppis, the variability is 

 accounted for by supposing the system to consist of two 

 bodies of nearly equal size, but differing slightly in 

 brightness, revolving in contact with each other. 



Bulletin No. 4 of the Lick Observatory, which has been 

 kindly forwarded by Prof. Campbell, gives an account of 

 recent results obtained with the Mills' spectrograph. To 

 the 25 spectroscopic binaries previously discovered are now 

 added six more, namely, w Cephei, o 31 Cygni, ^ Piscium, 

 T Persei, J Ceti, and s Hjdrae. An account is also given 

 of abservations which are in jirogress for a sjiectroscopic 

 determination of the period of the interesting telescopic 

 l)inary J Equulei, it being at present doubtful whether the 

 period is hi or 11"4 years. Continued observations of 

 Polaris indicate that the period od. 23h. 14'3m. completely 

 satisfies all the observations for the revolution of the 

 bright star round the centre of mass of itself and its dark 

 companion; they also show further changes which support 

 the conclusion that this jiair revolves round the centre of 

 mass of itself and a third body in a much longer period. 

 Deslandre's discovery that 5 Ononis is a sjiectroscopic 

 binary has been confirmed, but the observations which 

 have been made of a Persei do not confirm Mr. Newall's 

 conclusion that this is also a, spectroscopic binary. Another 

 note relates to the velocity of 1830 Groombridge, which 

 was mentioned in this column last month. In Bulletin 

 No. 3 there are details as to 94 new double stars, 33 of 



which were discovered by Mr. Aitken with the 36-inch 

 refractor, and the remainder with the 12-iiich. 



Further reports on the progress of the work for the 

 determination of the solar parallax 1)}' the recent observa- 

 tions of Eros are given in Circular No. 8 of the Conference 

 Astrophotographique Internationale. The problem is by 

 no means the simple one suggested by our elementary 

 text-books, and we gather that about two years must 

 elapse before the final result can Ije made k'uown. Much 

 of the labour involved is in getting the exact positions of 

 the comparison stars used in the measurement of the 



planet's position at different times. — A. F. 

 — •-•-• — 



Botanical, — In the current volume of the Journal of 

 the Limiean Society, Mr. I. H. Burkill has a jiaper on the 

 Flora of Vavau, one of the Tonga Islands, founded on a 

 collection of plants sent to Kew by Mr. C. S. Crosby. 

 This island, which has a remarkably rich vegetation, is 

 twelve miles long, and six miles across at its broadest part. 

 Its temperature ranges from 70'^ F. to 90'^ F., and the 

 annual rainfall is about 160 inches, as much as 9| inches 

 falling in one day. Mr. Crosby's collection consists of 

 2t)2 phanerogams and 27 vascular cryptogams; while 

 Mr. Hemsley, in his " Flora of the Tonga Islands," 

 published in the same journal in 1894, enumerates 303 

 phanerogams and 33 vascular cryptogams for the whole 

 group. It is interesting to note that 92 of the Vavau 

 plants also occur in the Sandwich Islands, which are about 

 3000 miles distant, A common weed in the Tonga Islands 

 is the sensitive plant (Mimosa pudica), which, Mr. Crosby 

 sayfe, "painfully reveals imperfections in the soles of one's 

 shoes, though a native walks over it unconcernedly." The 

 paper includes seven new species, three of which belong 

 to Eucjenia. — S. A. S. 



— »-♦-• — 



Entomological. — It is not generally known that some 

 caterjiillars are to be included among the insects that live 

 in friendly association with ants, yet in tropical countries 

 the larvae of " Blue " butterflies are often found under the 

 ants' protection, A similar association has lately been 

 oliserved in Switzerland by Prof, H. Thomann, who 

 describes (Arch. Sci. Phys. ef Nat. (G-eucve), Vol. X,, 

 1900, pp. 565-6) the habits of the ant Formica cinerea 

 with regard to the caterpillar of Lycxna anjns. The ants 

 riui about over the caterpillars' backs in numbers, 

 constantly touching them with their mandibles. They 

 protect the caterpillars from the attacks of Ichneumon 

 and Tachinid flies, and harbour the chrysalids in the 

 galleries of their nests, allowing the butterflies to emerge 

 unmolested. In return for these favours, the caterpillars 

 secrete from a thoracic gland a sweet thick liquid, of which 

 the ants seem to be very fond. 



American observers are still busy luiravelling the 

 mvsteries of ant-life on their continent. In the American, 

 Naluralist for March (Vol. XXXV., 1901, pp. 157-174), 

 Prof, Wheeler and Mr, Long describe the males of some 

 of the driver-ants (Ecitons) of Mexico, with notes on the 

 habits of the colonies. They ravage other ants' nests, 

 and convey the larvse to their own galleries to serve as 

 food, also they prey upon small ground-beetles. The 

 vii tims seem to be stored u]) for several days before being 

 devoured, and when the colony moves to a new nest the 

 contents of the larder are not left behind. 



In the Anterican Naturalist for May (t. c, pp, 337-356), 

 Mr. C. T, Brues describes two remarkable new genera of 

 small flies (Phoridte), One (Commoptera) was found in 

 a nest of the ant Selenopsis yeininata, in Texas, the other 

 (Ecitomyia) in a nest of Eciton, They resemble other 

 related flies found in similar situations in the reduction of 



