Dec. 1 6, 1880] NATURE 



Now if we write instead of tlie above — 



diMi' 



where k is some constant, it is evident that k will not depend on 

 the nature of the string but solely on the system of units employed 

 to express d, I, and T. 



If C.G.S. units be employed, we have, as stated in Prof. 

 Everett's translation of Deschanel — 



147 



livi' 



where m is the mass of unit length ; and as we may write instead 

 of m, Trr" s, r being the radius of the wire, we shall have — 



V^ 



VFr ^7'°'^-Tr Vj' 



so that here i = — i-r = '5642 approximately. 



With any other system of units we may of course determine i 

 from the value just given, by multiplying or dividing by the 

 ratios of the new to the C.G.S. units; for example, if J be 

 expressed in millimetres, / in metres, and T in kilogrammes, our 

 new constant would be — 



A I 10 1 ,— 



^ = V^ • T • T^ ■ "^981000 

 = ^-^J = 55-87. 



But we may also determine i directly for any system of units in 

 the following manner : — If, in the formula — 



al V s ' 

 we make <f, /, T, s, each unity, we shall have — 



Imagine then a wire of water, I mm. diam., I metre long, 

 stretched by a weight of I jkilo. : its weight would be 7854 

 grm., and jV, the "tension length," or length which would 



be equal in weight to the stretching weight, would be _- — 

 = 1273"2 metres. The velocity v of transmission o f a pulse 

 along the wire would be "^gH = ''^g-Si X 1273-2 = 11176 

 metres per second, and the number of vibrations per second — 



„=JL^ lIi:Z^ = 55-88 = k, 

 2 / 2 



the same figure as that obtained above. 



If the units in which d, I, and 7* are expressed are respectively 

 the tenth of an inch, the foot, and the pound, k becomes 48*66. 



In the later editions of Ganot's "Physics" we find the 

 formula — 



r82S7 /^/^ 



given, where c is the "tension length," and / the length of the 

 string, both expressed in inches. This formula would of course 

 be of more easy application than those given above when we 

 know the weight per foot of the string, but does not directly 

 show the relation of » to the diameter and specific gravity. 



W. J. Grey 

 Newcastle-on-Tyne J. T. Dunn 



The U.S. Weather Charts 



I SHOULD be much obliged if you would inform me whether 

 the United States Monthly Charts of Meteorological Data, 

 in continuation of the series published in Nature, can be 

 procured in London, and if so where. H. M. 



6, Charles Street, Grosvenor Square, December 7 



Climate of Vancouver Island 



Mr. Alfred R. Wallace asserts in his letter published in 

 Nature, vol. xxiii. p. 124, that the climate of Vancouver 

 Island is not so mild as that of London. 



For three years I commanded a gunboat on those shores ; 

 speaking from recollection, and not from recorded observations, 

 and with great deference to so distinguished a naturalist as Mr. 



Wallace, I should have said that the climate of Vancouver 

 Island was a good deal milder than that of London. 



Edmund H. Verney 

 Travellers' Club, Pall Mall, S.W., December 11 



Meteors 



On the evening of November 20 at about 8 p.m. my attention 

 was attracted by a number of meteors appearing as often a^ once 

 per minute in different quarters of the heavens, but pursuing 

 courses apparently radiating from a point near the constellation 

 Andromeda. M. A. Veeder 



Lyons, New York, November 22 



THE PROBABILITY OF PHYLLOXERA 

 CROSSING THE TROPICS 



MUCH alarm has been felt by the wine-growers of 

 .South Africa at the possibility of the phylloxera 

 being introduced into the Cape vineyards. Very stringent 

 regulations have been framed in consequence, prohibiting 

 the importation of living plants or vegetables in any form ; 

 and so rigidly have these regulations been carried out 

 that it is stated that, in accordance with them, a cargo of 

 potatoes from New Zealand was destroyed on its reaching 

 Capetown. 



It is generally conceded by the experts who have been 

 consulted that the importation of vines, on the tissues of 

 which the phylloxera would be able to live in transit, 

 must be prohibited. The phylloxera can however, it is 

 admitted, feed on no other -plant but the vine, and the 

 important question for the South African Government 

 to decide is whether it is really needful to exclude other 

 plants or vegetables besides the vine. In order to obtain 

 the best opinion upon this point, Dr. Alaxime Cornu was 

 consulted. He accordingly drew up several reports, in 

 which he expresses the opinion that, though extremely 

 unlikely, it is still theoretically possible that the phylloxera 

 should be conveyed from Europe to South Africa by 

 means of other vegetable products than the vine, and he 

 therefore supports the prohibitive action taken by the 

 Cape Government. 



The inconvenience to the community which such a 

 policy involves is necessarily considerable. The grounds 

 of Dr. Maxime Cornu's decision have therefore been 

 carefully considered by an entomologist who has studied 

 the subject and who has drawn up the following notes. 

 The question is of great importance to all wine-growing 

 countries in the southern hemisphere, and as these 

 doubtless contain inany readers of Nature, I think the 

 publication of these notes in its columns will give them 

 the best opportunity of being fairly considered. 



W. T. T. D. 



No/es on Dr. Cornu's Reports on the Phylloxera, and 

 on the Protective Measures against its Introduction. 



Among the " truths " laid down in the first report, No. 

 I. is, "The Phyllo.xera vastatrix lives only upon the 

 vine." This is emphasised in the third report (" Memo- 

 randum on Laws of Protection, &c."), Paragraph No. IV., 

 stating, " they (the insects) can, moreover, subsist only 

 upon the vine." 



Notwithstanding these unreserved statements of this 

 fundamental fact in the life history of phylloxera, the same 

 " Memorandum on Laws of Protection, &c.," proceeds (in 

 its '• General Conclusion ") to recommend, " if such acourse 

 were possible," the imitation of " the example set by 

 Algeria, and to forbid the introduction of all vegetable 

 products whatever, with the exception of those which are 

 absolutely required for consumption." 



It may well be asked on what ground such a recom- 

 mendation is based. After stating (Third Report, Para- 

 graph IV.) that the phylloxera cannot live when dis- 

 sociated from the vine for more than four or five days, 

 and requires protection from dcssication in any case, Dr. 



