May 1 6, 1878] 



NA TURE 



83 



After describing the apparatus used, and the locality where it 

 was erected, he explains the forces which act on an anemometer. 

 When these balance each other through a revolution, the condi- 

 tion of permanent motion is expressed by the equation 

 aV'^ — zfiVv — yv'^ — F = o. Where Fand v are the veloci- 

 ties of the wind and anemometer in miles per hour, F the 

 mDmentum of the friction, at the centres of the cups, in grains, 

 the coefficients o, fi, y, cannot be found ^ priori in the present 

 state of hydrodynamics ; but if they be constant, or vary but 

 little as V changes, they can be found, at least approximately, by 

 combining several equations in which Vv F are known. Unfor- 

 tunately this method has serious difficulties. We cannot produce 

 wind of a known V, and must substitute for it the transport of 

 the anemometer through the air at a known speed. But the 

 rotation of the whirling machine produces an air vortex of 

 considerable power, whose motion must be subtracted from that 

 of the machine. If this motion were uniform it would do no 

 harm, but it is found to be so very irregular that the V which 

 must be used is uncertain. 



The determination of F was also uncertain in these experi- 

 ments, chiefly because the locality where the apparatus was 

 erected (though the best which he could obtain) was affected by 

 tremors by the action of adjacent machinery which made the 

 frictions variable. Five anemometers were tried. No. i with 

 9-inch cups and 24-inch arms, the Kew type ; No. 2, the same 

 arms, bat 4-inch cups; No. 3, with 9-inch cups and 1 2-inch 

 arms ; No. 4, the same 12-inch arms and 4-inch cups ; and 

 No. 5, semi-cylinder cups 9 inches square and 24-inch arms. 

 Of these the small cups gave unsatisfactory results, the cylinders 

 (to his surprise) the best ; the 9-inch were sufficiently good to 

 authorise the following conclusions, observing that a was mea- 

 sured directly. It is as the area of the cups, and is independent 

 of the length of the arms, unless they are so short that the wake 

 of one cup interferes with the followers. 



1. The equation represents the observations well enough for 

 all practical piurposes, while Granges from 5 to 40, and F from 

 113103683. 



2. It is equally effective if 7 be omitted. 



3. j8 and 7 are probably proportional to a, and the three are 

 as the density of the air. 



4. Admitting this, the specialty of any anemometer depends 



on — only. 

 a 



,5. The ratio of the wind's velocity to that of cups changes 

 with V and F. The highest value in these experiments = 21 '58 ; 

 its least value = 2*32. 



6. With the constants which he found for the 9-inch cups, the 

 limit of this ratio, that for ?^ infinite = 2*30 instead of 3*0. 



He proposes to verify these conclusions with real wind, and 

 has established No. I near one of the Kew type similar to it. 

 By comparing their simultaneous 1/ under different frictions, he 

 will obtain equations which, assuming a as known, will, he hopes, 

 give /3 and 7 far more certainly. 



Mathematical Society, May 9. — Lord Rayleigh, F.R.S., 

 president, in the chair. — Messrs. Wm. Hicks and T. R. Terry 

 were elected members, and Prof. Minchin was admitted into 

 the Society. Messrs. Brioschi, Darboux, Gordan, Sophus Lie, 

 and Mannheim, were elected honorary foreign members. — Prof. 

 Henrici, F.R.S., communicated a paper by Dr. Klein, of 

 Munich, "Ueber die Transformation derelliptischen Functionen," 

 — Prof. Cayley, F.R.S. , spoke on the theory of groups. — Prof. 

 Kennedy read his notes on the solution of statical problems 

 connected with linkworks and other plane mechanisms. The 

 special object of this last paper was to give an elementary solu- 

 tion of the problem : given a linkwork or plane mechanism of 

 any number of links, with any force acting on any one of them, 

 find the magnitude of the force necessary to balance the me- 

 chanism of acting in any direction on any other link. The 

 method employed was the replacement of the two links on which 

 the forces acted by two others which had the same instantaneous 

 centres and the same angular-velocity ratio, but which were so 

 chosen that they could be directly connected together by a third 

 link. In this way a simple combination of the links was used 

 as a " virtual mechanism " to replace the original complex 

 linkwork, and the "solution became extremely simple. Inci- 

 dentally the author took occasion to insist on the advantages of j 

 the consistent use of the notion of the instantaneous centre even ; 

 in the most elementary treatment of mechanical problems. — Mr. : 

 Glaiiher, F.R.S., communicated a generalised form of certain 



series. — Mr. Kempe read a portion of his paper on conjugate 

 four-piece linkages. 



Linnean Society, April i8. — Dr. J. Gwyn Jeffireys, F.R.S. » 

 vice-president, in the chair. — The Rev, H. H. Higgins exhibited 

 photographs of a large beetle, the Dynasies neptunus, Shonherr, 

 and of an imdetermined species of locust from Borneo, the latter 

 resembling the genus Pseudophyllus, but measuring 9^ inches in 

 expanse of wings. — A paper on the geographical distribution of 

 the gulls and terns (Laridae) was read by Mr. Howard Saunders. 

 Notwithstanding the wide marine dispersion of the group, it 

 possesses several remarkable isolated forms. In numbers there 

 are about fifty-three species of terns and skinners, fifty of gulls,, 

 and six of Skua gulls. The majority of the typical Laridce are 

 found in the North Pacific, where alone the Arctic and white 

 primaried forms are connected through Larus glaucescens with 

 the group which have distinctly barred primary wing feathers. 

 In the same area can be traced the typical hooded gulls, of which 

 Z. ridibtmdus is the Palaearctic representative, and which in 

 L. glaucoides reaches unbroken to the Magellan Straits, while in 

 the eastern hemisphere it is not found beyond 10° N. lat. There 

 also obtains the peculiar coloured tern. Sterna aleutica, which 

 connects the typical Sternje wkh the intertropical sooty-terns^ 

 S. lunata, S. anastheta, and S. ftdiginosa. Of isolated groups 

 which have no apparent connection with the Pacific may be men- 

 tioned the New Zealand Larus bulleri and Z. scopnilinus, the 

 Australian Z. nova-hollandice and the South African Z. hartlaubi. 

 In the Arctic region there are two isolated specialised genera of 

 gulls, Pagophila and Khodostethia, which are not known on the 

 Pacific side, while amongst the terns the intertropical genera, 

 Nsemia, Anous, and Gygis, although somewhat related among 

 themselves, offer no particular points of union with the typical 

 Sterninje. It results that the bulk of the evidence favours the 

 idea of the North Pacific probably being the centre of dis- 

 persion of these chiefly oceanic or shore -frequenting birds, 

 the Larida;. — Mr. R. Irwyn Lynch next made a communication 

 on the mechanism for the fertilisation of Meyenia \erecta, Benth, 

 This West African acanthaceous shrub has a funnel-shaped 

 corolla with hairy anthers midway in the tube. The longer 

 slender flexible style has its double-lipped stigma so formed and 

 placed that insects alighting and entering towards the nectar at 

 the bottom of the flower on their retiurn, so move the lever-lip 

 of the stigma as to produce pollenisation. — Mr. J. Clark Hawk- 

 shaw brought forward some notes on the action of limpets 

 (Paiella) in sinking pits in, and abrading the siu-face of the chalk 

 at Dover, The limpet tracks are finely-grooved hollows gene- 

 rally of a zigzag pattern varying from eight to fourteen inches 

 square, and about a line deep ; and according to the author 

 produced by the lingual teeth of the animal while grazing on the 

 fine coating of sea-weed which covers the face of the chalk. The 

 grooving deepens as the creatures repeat the process over the 

 same ground ; they moreover sink deeper stationary basin-shaped 

 pits, resting-places to which they return after feeding. These 

 latter, he holds, are also formed by mechanical, and not chemical 

 agency, as some contend. Though taken singly, the denudation 

 of the chalk by the limpets is very insignificant, yet taken in the 

 aggregate, the amount annually abraded must be very consider- 

 able. — The following gentlemen were balloted for, and duly 

 elected Fellows of the Society : — The Rev. A. A. Harland, the 

 Rev. J. J, Muir, Mr, W. S. Piper, and Mr. Fred, Townsend. 



Meteorological Society, April 17. — Mr. C, Greaves, pre- 

 sident, in the chair. — Mons. Marie Davy, Capt. N. Hoffmeyer, 

 Prof. D, Ragona, and Dr. A. Wojeikoff", were elected honorary 

 members. — The discussion on waterspouts and globular lightning, 

 which was adjoiu-ned from the last meeting, was resumed and 

 concluded. — The following papers were then read: — On the 

 application of harmonic analysis to the reduction of meteoro- 

 logical observations, and on the general methods of meteorology, 

 by the Hon, R. Abercromby, F.M.S. The meaning of the 

 harmonic analysis is first shown, in reference to average baro- 

 metric pressure, by tracing the geometrical and physical signifi- 

 cance of every step from the barogram till the tabidated results 

 are combined in a harmonic series. It is then shown that, 

 whether we regard this series simply as an algebraic embodiment 

 of a fact, or as a series of harmonic components, as suggested by 

 Sir W, Thomson, it is simply a method of averages, and our 

 estimate of its value must depend upon an estimate of the use of 

 averages at all in meteorology. It is then pointed out where 

 averages are useful, and their failure to make meteorology an 

 exact science is traced to three causes: (i) That the process of 



