July 20, 191 1] 



NATURE 



71 



calculate it before we can arrive at the true bending effect. 

 It the material is homogeneous and elastic, the vertical 

 Bane of steepest slope at any place contains the direction of 

 ill.- resultant gravitational force. But while the gravila- 

 fonal - ffect must be as instantaneous as gravity itself, the 

 bending effect will show a lag unless the material is per- 

 fectly elastic, so far, at least, as tidal load is concerned. 

 It is manifestly a case in which measurement of the 

 apparent slope in two perpendicular planes is likely to add 

 materially to knowledge. An estimate which I made in 

 1S96 for the effect of tides in the Thames at Kew Observa- 

 i..ti, assigning the low value of iixio 7 grammes weight 

 per sq. cm. to the rigidity, and assuming the material 

 incompressible, made the difference of the slope between 

 •extreme high- and low-water only of the order o"-05, and 

 so too small to be measured satisfactorily by the Milne 

 seismograph at the observatory. Charles Chree. 



July 15- 



Hamilton and Tait. 



It mav at first sight seem a little ungracious to take 

 exception to a statement in the extremely gratifying review 

 of the "Life and Scientific Work of P. G. Tait," which 

 "A. G." contributed to Nature of July 13. But the point 

 is one which brings out in a remarkable degree the great 

 modesty of Tait in regard to his own achievements. Your 

 reviewer says that Tait " was introduced by Andrews to 

 Rowan Hamilton, at that time in the full tide of his quater- 

 nion work, and busy with the preparation of the ' Elements ' 

 for publication." 



Now it is, I think, clearly established in the "Life," by- 

 means of quotations from Hamilton himself, that when the 

 correspondence with Tait began Hamilton had stopped 

 working at quaternions, that the correspondence drew 

 Hamilton back to the study of his calculus, and that, as I 

 put it in the "Life," p. 132, it was Tait "who fired Hamil- 

 ton with the ambition to write his second great ' Treatise 

 on Quaternions.'" This is proved by Hamilton's own 

 words, quoted on p. 131 of the "Life." Since possibly 

 many readers may not be interested in the quaternion side 

 of Tait's activities, I take the liberty of reproducing this 

 -quotation here. Writing on January 21, 1859, Hamilton 

 remarked : — 



"As to myself I cheerfully confess that I consider myself 

 to have, in several respects, derived advantage, as well as 

 pleasure, from the correspondence. It was useful to me, 

 for example, to have had my attention recalled to the 

 whole subject of the quaternions, which 1 had been almost 

 trying to forget ; partiy under the impression that nobody 

 cared, or would soon care, about them. The result seems 

 likely to be that I shall go on to write some such ' Manual,' 

 not necessarily a very short one — as that alluded to in a 

 recent paragraph." 



It seems clear that without the Tait correspondence. 

 Hamilton would never have undertaken the second 

 treatise. This was one of the discoveries which I was 

 privileged to make when the correspondence was committed 

 to my c.ire. To me it was a very surprising discovery. I 

 had often conversed with Tait about his relations with 

 Hamilton — and he was critical as well as appreciative in 

 these reminiscences — but I never heard him sny anything as 

 to the part he played in the first beginnings of the 

 "Elements." In his own writings, such as the prefaces to 

 the successive editions of his treatise, or the biographical 

 notices he wrote of the great Dublin mathematician, Tait 

 had ample opportunities of telling the story of his intimate 

 connection with Hamilton's second treatise. But not the 

 least hint was ever given. It may be that Tait felt his 

 hands tied because of the absence of any reference in the 

 " Elements " to the correspondence. But we must remember 

 that Hamilton did not live to complete his work or to 

 write more than the merest fragment of a preface. Now 

 that we know the truth from Hamilton's own letters, the 

 whole episode is a fine example of Tait's modesty, and even 

 self-effacement, in regard to his influence in shaping 

 scientific development. The story throws such a beautiful 

 light upon the character of Tait that I am sure your re- 

 viewer will thank me pointing out the one slight inaccuracy 

 in 'in otherwise perfect review. C. G. Knott. 



Edinburgh University, July 17. 



NO. 2177, VOL. 87] 



The fruiting of the Tamarisk. 



This exceptional season is having strange effects on many 

 of our native plants and animals, and naturalists would do 

 well to note these before it is too late. 



For many years 1 have tried without success to find 

 Tamarix anglica in fruit in Britain. The absence of fruit, 

 and the rarity of the tamarisk except where obviously 

 planted, seemed to support the idea that it was of fairly 

 modern introduction. 



A few years ago, however, fragments of rope, found in 

 Roman Pevensey and sent to Kew, were pronounced to be 

 formed in part from the inner bark of tamarisk. This 

 seemed to favour the inclusion of the tamarisk in the 

 British flora, though rope found in a Roman seaport may 

 quite well have been manufactured abroad. 



This season the negative evidence yielded by the absence 

 of seed has also broken down ; and if a plant seeds once in 

 its lifetime, it may hold its own and establish its right to a 

 place in our flora — as the Cornish elm has done. 



I planted last spring some young tamarisks on a steep 

 bank of loose sand in my garden at Milford. During the 

 long drought they received no water ; they are now seeding 

 freely, and the winged seeds are being dispersed by the 

 wind. If the plant reproduces itself from these seeds, sown 

 under natural conditions, the cycle will be complete ; but 

 the garden is a quarter of a mile from the sea, and the 

 test may be too severe a one. 



Tamarisk is essentially a desert and sea-coast plant, and 

 it would be worth while' to examine any tamarisks growing 

 on sand-dunes, to see whether they also are seeding, and to 

 see whether seedlings come up. Possibly the tamarisk may 

 be a survivor from times when desert or " loess " conditions 

 extended over western Europe. We have found the fossil 

 remains of many of the desert animals, but plants decay 

 in porcus deposits of dust, and desert plants are seldom 

 washed into ordinary alluvial deposits. Clement Reid. 



Milford-on-Sea, Hampshire. 



Sunshine and Fleas. 



Aristotle (H.A. viii. 6051!.) makes the following curious 

 and perplexing statement :— Travra 5e to fvro/ia anoBv^aK^ 

 iXatovneva- -raxiara i>', fie Tis tiji/ KetpaXri" aAetyas iv T<i> 

 jjA.V flfi. That is to say : " All insects die if they be smeared 

 over with oil ; and they die all the more rapidly if you 

 smear their head with the oil and lay them out in the sun." 

 So Pliny, Albertus Magnus, and recent commentators read 

 and interpret the passage. But in the former half of the 

 sentence, for tAa'ovixei'a, several MSS. read i)\mip.iva : i.e. 

 not "if they be smeared with oil," but simply "if they be 

 exposed to 'the sun " ; while in the latter half there is an 

 obvious ambiguity, which inclines me to think that 

 ret !VTo,ua is used sensu restricto, and that tV Ke<pa\7iu 

 refers, not to the insect's head, but to the experimenter's. 



I take it, in short, that the heat of the sun was the 

 main agent recommended for the destruction of the insects, 

 and it is interesting to find this agency again coming into 

 practical use for a very similar purpose. One of the latest 

 of the Indian Medical Department's "Scientific Memoirs," 

 by Capt. J. Cunningham, is entitled "On the Destruction of 

 Fleas by Exposure to the Sun." The writer recommends 

 the wholesale disinfection of clothing and baggage, for the 

 special purpose of destroying plague-carrying fleas, by the 

 simple process of laying out the garments or bedding on 

 a sandy floor, exposed to the full rays of the sun. The 

 author has made many careful and elaborate experiments, 

 and has succeeded in showing that in less than an hour's 

 time, under an Indian sun, the fleas are all dead. 



D'Arcy W. Thompson. 



The Oban Pennatulida Again. 



Marine biologists may be interested to hear that the bed, 

 near Oban, of the largest British pennatulid Funiculina 

 quadrangularis, and the smaller Virgularia mirabilis de- 

 scribed by Mr. W. P. Marshall and the late Prof. Milnes 

 Marshall in 1881 or 1882 (I have no books of reference with 

 me) is still apparently in very flourishing condition. In 

 a couple of hauls of the small Agassiz trawl, from this 

 yacht yesterday, between the islands of Kerrera and Lis- 

 more, at depths of eighteen to twenty fathoms, I got about 



