148 



NATURE 



[March 31, 1910 



larva of Cnethocanjpa pinivora. The processionary habits 

 of the larva of this moth — which is abundant in the pine 

 woods of the neighbourhood of Bordeaux — were first studied 

 by Reaumur in 1736, and again by Fabre in the latter half 

 of the last century. Both these writers describe the life- 

 history and habits of the insect in considerable detail. The 

 present paper, which is a summary of observations made 

 during a fortnight spent at Arcachon, is an attempt to sup- 

 plement these accounts by supplying information on certain 

 points which still remain obscure. The procession is one 

 of single file, the whole moving along a silken thread 

 which is commenced by the leader and added to by all the 

 larvae in succession. The author found that though any 

 larva could function as leader, yet the leader was capable 

 of taking a real initiative in cases, such as the selection of 

 a path, burrowing for pupation, &c., the satellites following 

 him whether influenced by the same stimuli or not. The 

 " circulating mass " is a formation which the larvae fre- 

 quently adopt when on the march. It consists in an 

 assemblage of larvae moving among each other, the mass, 

 as a whole, remaining stationary. A " circulating mass " 

 is always formed before the larvae burrow for pupation. 

 The leader appears to start the process of formation by 

 assuming a zig-zag mode of progression, which is followed 

 by the satellites. Though the order is completely broken 

 up within the mass, yet it was found in every case observed 

 that the leader of the procession which was re-formed 

 from it was identical with that of the original procession. 

 This was ascertained by marking the larvae by means of 

 fine sand or flour scattered over the dorsal papillae. Pupa- 

 tion occurs beneath the ground, and is complete about 

 nineteen days after burrowing. The burrowing is a 

 collective process, in which all the larvae within a circu- 

 lating mass take part. — Prof. W. Burnside : Double sixes. 

 — H. Bateman : The solution of a system of differential 

 equations occurring in the theory of radio-active trans- 

 formations. — Dr. Youne : The change of order of integra- 

 tion in an improper repeated integral. — R. T. Beatty : 

 The production of kathode particles by homogeneous 

 Rontgen radiations. The kathode particles produced when 

 these radiations pass through a thin silver leaf are absorbed 

 by air, so that their coefficient of absorption is a linear 

 function of the coefficient of absorption in aluminium of 

 the exciting radiations. The total energy of the kathode 

 particles set free in the leaf is proportional to the absorp- 

 tion by the leaf of the radiations. The range of these 

 particles in hydrogen relative to that in air increases with 

 the speed of the particles from 5 to 8. The total ionisation 

 produced by any bundle of these kathode particles when 

 totally absorbed in hydrogen is the same when air replaces 

 hydrogen. — Sir J. J. Thomson : The scattering of rapidly 

 moving electrified particles by matter, and its application 

 to the determination of the number of corpuscles in the 

 atoms of the various elements. An expression for the 

 scattering of a pencil of rapidly moving electrified particles 

 is found by the following method. First calculate the 

 average deflection of the direction of motion of an electrified 

 particle when passing through an atom which is assumed 

 to consisi of a large number of corpuscles placed in a 

 sphere of uniform positive electrification ; the expectation 

 of any angular deflection after a large number of particles 

 have passed through a large number of atoms can then be 

 found by the theory of probability. In this way it is 

 shown that the average angular deflection when a pencil 

 of rapidly moving particles passes through a thin plate 

 of thickness t is 



m?^ \ 



A.N.( 



64No+'VNo 

 10 



where v is the velocity of the particle, e the charge, and 

 m the mass of the particle, N the number of atoms in unit 

 volume of the plate, and N, the number of corpuscles in 

 each atom in the plate ; hence if we measure the scattering 

 of such a pencil we can determine the value of N,. 



Manchester. 



Literary and Philosophical Society, February 22. — 



Mr. Francis Jones, president, in the chair. — A. Brothers : 



Halley's comet as seen in 1835, compared with Donati's 



in 1858. Good drawings or sketches of Halley's comet 



NO. 2109, VOL. 8t,] 



seem to be rare. Sir John Herschel saw the comet at the 

 Cape of Good Hope, and from his sketches it was not 

 very conspicuous. Struve in 1835 gives a sketch which 

 shows it to have been bright, probably when it was near 

 the sun, but as a brilliant object it must have been very 

 inferior to several which were seen during the nineteenth 

 century. The author has a distinct recollection of seeing 

 the comet in 1835. The object certainly was not so bright 

 as Struve shows it to have been, and still greatly inferior 

 to Donati's comet. It is generally spoken of now as likely 

 to appear as a brilliant object, but the author points out 

 that there is little evidence for the assertion. — Dr. H. F. 

 Coward : The inflammability of gas-mixtures. Hydrogen 

 and oxygen mixtures were shown to be capable of in- 

 flammation at a much lower pressure than had been 

 imagined previously if the igniting spark were produced 

 in the most suitable manner. Minima for sparks of 

 various nature with electrodes of various kinds were given. 

 March 8. — Mr. Francis Jones, president, in the chair. — 

 D. M. S. Watson : Upper Liassic Reptilia, part ii., the 

 Sauropterygia of the Whitby Museum. The chief Plesio- 

 saur in the Whitby Museum is the type-specimen of 

 Plesiosaurus propinquus, Blake. This is re-described in 

 the present paper. It is a member of the large-headed 

 group of Plesiosaurs, but differs considerably from other 

 Liassic species, such as " Thaumatosaurus " megacephalus 

 (Stutchbury) and Rhomaleosaurus cramptoni (Baily and 

 Carte). It may possibly be necessary to found a new 

 genus for the species. The other remains consist of small 

 groups of vertebrae, one set of which, containing fifteen 

 cervicals of Sthenarosaurus dawkinsi (Watson), may be 

 Owen's type-specimen of Plesiosaurus coelospondylus, — 

 Sir W. H. Bailey : Mr. Myring's recent discoveries of pre- 

 historic pottery in Peru. Mr. Hewitt Myring, a 

 mineralogist and mine owner, visited the Chincuna Valley 

 in Peru, and explored some sand ridges with the view of 

 finding something in the Inca graves. The valley, how- 

 ever, had been used as a cemetery, not by the Incas, but 

 bv the Chimus, who preceded them in the occupation of 

 the country, and the work of exploration brought^ to light 

 several hundred pieces of pottery of great variety and 

 interest. The pieces are well preserved, owing to the 

 absence of rain and the consequent dryness of the soil. 

 This pottery, some of which recalls that of China,_ India, 

 and Egypt, shows great care, skill, and art, especially in 

 the modelling of the human face, and is remarkable in 

 that no two pieces are alike, a fact which demonstrates, 

 the author thinks, the intellectual liberty and original 

 genius of these early craftsmen. The age of the pottery 

 is not known, and may be several thousand years. About 

 one-third of the pieces discovered have been secured for 

 the British Museum, and it is hoped that shortly some 

 portion of the collection may find a permanent home in 

 Manchester. 



Edinburgh. 



Royal Society. February 7.— Dr. J. Burgess, vice-president, 

 in the chair. — Prof. Cossar Ewart : The short-tailed 

 domestic sheep. — Principal Laurie : Electromotive force of 

 cells with a single salt and two solvents. The paper gave 

 some preliminary results with cells in which potassium 

 iodide was the salt and water and alcohol the solvents, 

 as, for example, the relation of the electromotive force to 

 the strengths of the solutions, the variation with tempera- 

 ture, and the connected thermal properties, &c. In co- 

 ordinating the curious results obtained, the author brought 

 forward some suggestive views as to the distribution of 

 molecular energy in the two solutions. — Prof. F. G. Baily : 

 A stereoscopic optical illusion. When two objects are 

 nearly in the line of vision, so that when one is clearly 

 focussed the other appears as two images, one on each 

 side of it, this clearly focussed object appears to be, under 

 certain conditions, distinctly nearer to the observer than 

 it really is. The phenomenon was noticed accidentally, and 

 a careful study showed that it occurred only for a certain 

 range of distances. It was evidently a physiological effect. 

 — Drs. E. P. Cathcart, J. Gray, and A. Black : A new 

 form of respitory respiratory calorimeter for physiological 

 purposes. The temperature of the entering and issuing ajr 

 was measured by platinum thermometers or thermoelectric 

 junctions, the whole being under perfect automatic control. 



