October 27, 1892J 



NATURE 



611 



LETTERS TO THE EDITOR. 



[ I'he Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of NATURE. 

 No notice is taken of anonymous comtnunications.'\ 



Further Notes on a recent Volcanic Island in the 

 Pacific. 



The volcanic island — Falcon Island— in the Tonga group in 

 the Pacific, of the recent appearance of which an account is 

 given in Nature, Vol. xli., p. 276, has recently been passed 

 by a French vessel of war, the Duchaffaiilt, which reports that 

 the island is not now more than 25 feet high. 



In October, 1889, when examined by Commander Oldham, 

 it was 153 feet high, and a little over a mile long. Nearly 

 entirely composed of ashes, it was rapidly washing away, and by 

 the account above, it would seem that more than one-half the 

 island must now have disappeared. W. J. L. Wharton. 



October 20. 



Earth-fractures and Mars " Canals." 

 On seeing the figure of the so-called "canals "of Mars, pub- 

 lished in Nature of a few weeks back, I was at once reminded 

 of the pattern assumed by the cracks of glass broken by torsion, 

 as in Daubree's well-known geological experiment. 



I enclose a photograph of part of a large slab of glass broken 

 in this way in a class experiment of my own, and although other 

 slabs, which have unfortunately not been preserved, exhibited, if 

 I remember rightly, still more Martial-looking networks, I think 

 that the general resemblance is obvious enough in this case. 



It may perhaps be well to explain to non-geological readers of 

 Nature that Daubree's glass-breaking^ is regarded by many as 

 reproducing in miniature the kind of fractures which are found 

 to occur in those portions of the earth's crust with which we are 

 acquainted, and that by tor.Nion only has it proved possible to 

 imitate the peculiar pattern assumed by such fractures, whether 



they be joints or dislocations. It is further held by many that 

 lUch lines of fracture in such patterns are a necessary result of the 

 hrinking of the outer coat of a planet in course of cooling. 



Mere fractures, such as we meet with in our own planet, 

 could, of course, not be seen Irom any considerable distance, 

 and if the circumstances of denudation were the same in Mars 

 as with us, the "canals" could certainly not be the representa- 

 tives of our usually hidden and featureless earth-cracks. There 

 seems, however, to exist, in the extraordinarily rapid melting of 

 gigantic ice-fields described by Prof. Norman Lockyer, some 

 evidence of denuding power in Mars on a scale enormously larger 

 than is the case with us. Earth-fractures — and for the matter of 

 that Mars-fractures too — must many of them be lines of weakness 

 along which denudation acts more freely than elsewhere, and 

 if this denudation be phenomenal and cataclysmic, as appears 

 to be likely in Mars, wide valleys or channels capable of being 

 distinguished at great distances would soon be scoured out along 

 them. 



' Not " zV^breaking " as a mistranslation of the word " g!ace " lias caused 

 it to be described in some Eneiish text-books. 



>JO. T200. VOL. 46] 



1 would wish especially to draw attention to the three follow- 

 ing points observable in the photograph, viz., the two marked 

 directions in which the crack-lines run, one set crossing the others 

 often at, or very nearly at, right angles ; their occasional 

 doubling and rough parallelism for some distance ; and their 

 frequent sudden stoppage— three of the features most noticeable 

 in the Mars lines. G. A. Lebour. 



Durham Coll. Science, Newcastle, October 13. 



A Wave of Wasp-Life. 



Mr. Hudson's charming work on " The Naturalist in La 

 Plata " reminds me of a very interesting wave of wasp-life which 

 appeared in Wisconsin in the summer of 1886. We were living 

 at the time in our summer-house at Pine Lake, and were 

 making observations on the habits of the different animals in the 

 neighbourhood. 



In the latter part of July we suddenly found ourselves sur- 

 rounded by large numbers of yellow-jackets and hornets. 

 Everywhere through the woods and fields a veritable plague of 

 wasps seemed to have descended upon the earth. During all 

 the month of August we heard the same report from summer 

 residents within a radius of twelve or fifteen miles of Pine Lake. 

 In our immediate neighbourhood we knew of forty-seven nests. 

 Allowing 1500 wasps to a nest — a very low estimate for that 

 season of the year — this gave us over 70,000 wasps. Plates of 

 meat and bones that were set outside for the cats were 

 immediately covered with them, and in spite of screens in doors 

 and windows they even entered the house, alighting on the food 

 at the dinner-table, or darting about and catching flies. 



The cause of this sudden increase in the number of wasps was 

 evidently a general one, since it acted in the same way upon 

 three species — Vespa vidua, V. maculata and V. germanica. 

 An examination of the Signal Service statistics does not show 

 anything unusual in the preceding winter and spring, but either 

 the weather must have been especially favourable, lessening the 

 ordinary death-rate of the queens, or there must have been a 

 marked decrease in the parasites or other enemies which 

 ordinarily keep these species in check. 



The duration of the favourable conditions proved brief 

 enough. It is probable that every one of our forty-seven nests 

 furnished, at the very lowest estimate, one hundred developed 

 and fertilized queens to start forty-seven hundred new nests in 

 the following year ; yet the increase in the checks to the too 

 great ascendency of these species more than counter-balanced 

 the abnormal increase. The winter of 1886-87 was not especially 

 severe, but in the following summer the most careful search 

 on our part, and on the part of others, whose efforts were stimu- 

 lated by the offer of rewards, only gave us four nests in our 

 neighbourhood, and on all sides we were met by the inquiry : 

 " What has become of the wasps ? " 



G. W. Peckham. 



Milwaukee, Wisconsin, October 12, 



Note on the Occurrence of a Freshwater Nemertine 

 in England. 

 A FEW days after reading M. de Guerne's "History of 

 Freshwater Nemerteans," published in the August number of 

 the Annals, I happened upon a specimen of the group amongst 

 the roots of some water plants, which I collected in the river 

 Cherwell, close to Oxford. I was, at the time, searching for 

 the cocoons of a new Rhinodrilid worm, of which a description 

 will shortly appear. The gathered roots, with the cocoons, 

 were placed in a bottle of water, in order that the worms might 

 hatch out. On examining the bottle two days later, namely, on 

 September 5, I noticed a small bright orange animal, about half 

 an inch long when extended, creeping amongst the cocoons. 

 Further observation with the microscope showed that it was 

 a species of Tetrastemma. Unfortunately the animal was 

 crushed before I had done more than sketch the general ap- 

 pearance and make some few observations, and I have not yet 

 succeeded in finding more specimens ; so that I am unable to 

 state how far it agrees with or differs from the previously known 

 freshwater forms enumerated by M. de Guerne, most of which 

 are included by Silliman and later authors under the title 

 Tetrastemma aquarum dulcium. 



In one or two points, however, my sketches show certain 

 differences from those of Silliman : — 



