5i8 



NATURE 



[September 30, 1897 



species, if such exist, in which the caste distinctions are 

 still incipient. If it can be shown that the evolution of 

 caste characters is in any way anterior to the loss of 

 fertility, the difficulties of interpretation will disappear ; 

 at present the evidence points to the fact that owing to 

 qualitative changes in nutrition, rather than simple mal- 

 nutrition, an atrophy of the sexual organs is set up which 

 is correlated with a hypertrophic modification of other 

 structures, by a deflection, so to speak, of the nutritive 

 stimulus. 



Many neoteinic forms show no trace of wings. If the 

 termite colony were headed by such forms only, the 

 phenomenon, as Grassi points out, would occasion no 

 surprise, but all valid evidence would be wanting that 

 the species had ever possessed wings. This leads to the 

 admission on his part that there is no proof that all 

 existing wingless insects may not be descended from 

 winged ancestors, and in the absence of such a proof he 

 is led to reject Brauer's division of Insecta into Aptery- 

 gogenea and Pterygogenea. 



Space forbids any reference to the full account of the 

 social life, habits and instincts of the species which Prof. 

 Grassi has studied. Their intelligence, though remark- 

 able, is far inferior to that of ants, and may be profitably 

 contrasted therewith. Whilst referring to this subject, it 

 may be worth while to call the attention of those inter- 

 ested in animal psychology to two lately-published pam- 

 phlets on the subject, particularly that on the psychology 

 of ants,^ by Father Wasmann, a most careful observer 

 and thorough student of animal intelligence. 



One practical result of Grassi's work requires mention. 

 An isolated group of ten or a dozen Termites, containing 

 any forms which have not begun to undergo the atrophic 

 changes induced in the sterile castes, is capable of 

 converting such forms into reproductive individuals ; 

 and the little society, thus started, possesses the power 

 of multiplying into a large colony. 



It is therefore hopeless to attempt the extermination of 

 Termites merely by the destruction of the kings and 

 queens. W. F. H. Blandford. 



PERIODICAL COMETS. 

 'T'HE number of comets of short period which are 

 -*• expected to return to perihelion during the next 

 two years is remarkable. In 1898 the following comets 

 are due : — Pons-Winnecke (April), Encke (May), Swift, 

 1889 VI. (June), Wolf (June), Tempel, 1867 II. (Septem- 

 ber) ; in 1899, Denning, 1881 V. (January), Tempel, 1866 

 I. (March), Barnard, 1892 V. (April), Tuttle, 1858, I. 

 (May), Holmes (May), and Tempel 1873 II. (July). In 

 addition to these, 1898 may possibly witness a return of 

 Biela's comet, last seen in 1852, and of Coggia's, 1873 

 VI. ; but these are doubtful, and the prospect of re- 

 observing them appears to be very limited. Thus there 

 are thirteen known comets which may present them- 

 selves for detection, but several of them will be enabled 

 to elude observation in consequence of their unfavour- 

 able position, and in one or two cases the objects may 

 escape owing to the uncertainty now existing as to the 

 exact periodic times. 



Apart from the large number of interesting comets 

 which are likely to be visible, several fine meteoric 

 showers will probably occur, for the Leonids are due in 

 considerable abundance on November 14, 1898, 1899 

 and 1900, while the Andromedes ought to reappear on 

 November 23, 1898. Both for the cometary and meteoric 

 observer we are, therefore, entering upon a period very 

 prolific in important phenomena. 



During the first quarter of the present century the 

 number of cometary discoveries averaged about one per 



1 " Instinct und Intelligenz im Thierreich," .ind " Vergleichende Studien 

 iiber das Seelenleben der Ameisen und der hohern Thiere," by Erich Was- 

 mann, S.J. (Freiburg, 1897). 



NO. 1457, VOL. 56] 



annum. The present average is about five, including 

 periodical comets, which represent no small proportion 

 of the whole. The rapid increase, during the last twenty 

 years, in the number of comets of short period is very 

 striking, and proves not only that these bodies are ex- 

 ceedingly plentiful, but also that the field of discovery is 

 not nearly exhausted. They belong to the Jovian family, 

 with periods ranging from five to nine years. Encke's 

 comet furnishes rather an exceptional case, the period 

 being only y2) years, and considerably shorter than that 

 of any other known. 



Perhaps it may be interesting to make a brief seriatim 

 reference to the expected comets of the next two 

 years : — 



Pons-Winytecke.— IXviS comet, due in April 1898, was 

 well observed at its last return to perihelion in June 1892. 

 The ensuing' return will not be so favourable, as the 

 comet will be much more distant from the earth, and 

 visible only in the morning sky. This return will be 

 much the same as in 1875, foui" periods of the comet 

 being equal to twenty-three years ; thus perihelion 

 occurred on June 30, both in 1869 and 1892. 



Encke. — Returns in May 1898. The comet will not be 

 so well placed, owing to its southern position, as at its 

 last return, when it was quite conspicuous in December 

 1894 and January 1895. Observations may be made 

 satisfactorily from the southern hemisphere after the 

 perihelion passage, as in 1832 and 1865, when the comet 

 was discovered in June. At intervals of thirty-three 

 years ( = 10 revolutions of the comet) it comes to peri- 

 helion at nearly same times as before, and its apparent 

 path in the heavens is repeated. 



Swiff, 1889 VI. — Considerable uncertainty is attached 

 to the orbit of this comet. Hind deduced a period of 

 8'534 years, which would bring the comet back at mid- 

 summer 1898 ; but Coniel has more recently determined 

 the period as 892 years, with an uncertainty of 09 year. 

 If this object is redetected, it will probably be picked up 

 accidentally by some one engaged in comet-seeking. 

 The most favourable returns are those when it reaches 

 perihelion in October or November. 



lVolf.—Th.\?, comet, which will reach its perihelion in 

 June 1898, was favourably observed in 1884 and 1891 ; but 

 in 1898 the conditions are not nearly so good. The fol- 

 lowing ephemeris for the next return is by A. Berberick 

 {Ast. Journal, 253). 



R.A. Dec 



Date. h. m. „ , Light. 



1898. — lune 3 ... I 42-3 ... -h 18 18 ... 17 

 July 5 ... 3 18-3 ... +19 43 ••• 2-1 

 Aiii,'. 6 ... 4 49-3 ... +16 51 ... 2-3 

 Sept. 7.6 4'9 ... +10 2 ... 2'4 

 Oct. 9 ... 6 56-9 ... -r o 38 ... 2-4 

 Nov. 10 ... 7 17 9 ... - 9 21 ... 2*4 

 Dec. 12 ... 7 4-1 ... -16 20 ... 2'i 

 1899.— Jan. 13 ... 6 341 ... -16 31 ... 1-4 

 (Brightness May i, 1891 = i.) 



Dr. Berberick remarks that later returns of the comet 

 will be unfavourable. Seven of its revolutions are equal 

 to three of Jupiter, and a second approach of these bodies 

 will occur in 1922-23, depriving us perhaps of the sight 

 of the comet for a long time, if not for ever. 



Tetnpel, 1867 II. — Comes to perihelion in September 



1898. This comet was re-observed in 1873 ^"^ 1879, but 

 has not been seen since, though it has twice returned to 

 perihelion in the meantime. The conditions in 1898 are 

 not very good. The periodic time was about six years in 

 1867, 1873 and 1879 ; but perturbations by Jupiter have 

 considerably lengthened the period according to Gautier. 

 It is most important that the comet should be redetected 

 if possible. 



Denning, 1881 V. — Returns to perihelion in January 



1899, but under circumstances not nearly so favourable 

 as in 1 88 1. In January and February its distance from 

 the earth will be about 100 millions of miles, and about 



