July 9, 1903] 



NATURE 



237 



need not trouble about the self-contradictory statements of 

 the aims and the objects of the new institution with which 

 they were favoured by enthusiastic amateurs. 



A VACATION course in practical and clinical bacteriology 

 will be held at King's College, London, commencing 

 Wednesday, August 5, and ending Saturday, August 15. 

 Names must be sent in as soon as possible to the secretary 

 or to Prof. Hewlett. 



SOCIETIES AND ACADEMIES. 



London. 



RoyAl Society, June 11.— "On the Propagation of Tremors 

 over the Surface of an Elastic Solid." By Horace Lamb, 

 F.R.S. 



The paper treats of the propagation of vibrations over 

 the surface of a " semi-infinite " isotropic elastic solid, i.e. 

 a solid bounded only by a plane. For purposes of descrip- 

 tion, this plane is conceived as horizontal, and the solid as 

 lying below it. 



The vibrations are supposed due to an arbitrary appli- 

 cation of force at a point. In the problem most fully dis- 

 cussed this force consists of an impulse applied normally 

 to the surface ; but some other cases, including that of an 

 internal source of disturbance, are also considered. Owing 

 to the complexity of the problem, attention is concentrated 

 for the present on the vibrations as they manifest them- 

 selves at the free surface, and the modifications which' 

 the latter introduces into the character of the waves pro- 

 pagated into the interior are accordingly not examined 

 minutely. 



The investigation claims interest on theoretical grounds, 

 and also in relation to the phenomena of earthquakes. 

 Attempts to interpret seismic phenomena by the light of 

 elastic theory have hitherto been based, for the most part, on 

 the general laws of wave-propagation in an unlimited 

 medium, as developed by Green and Stokes ; but Lord Ray- 

 leigh's discovery of a special type of surface-waves has 

 made it evident that the influence of the free surface in 

 modifying the character of the vibrations is more definite, 

 and more serious, than had been suspected. The present 

 memoir seeks to take a further step in the adaptation of 

 the theory to the actual conditions, by investigating cases 

 of forced waves, and by abandoning the restriction to 

 simple-harmonic vibrations. 



It is found that the surface disturbance produced by a 

 single impulse of short duration may be analysed roughly 

 into two parts, which we may distinguish as the " minor 

 tremor " and the " main shock," respectively. The minor 

 tremor sets in at any place, with some abruptness, after 

 an interval equal to the time which a wave of longitudinal 

 displacement (in an unlimited medium) would take to 

 traverse the distance from the source. Except for certain 

 marked features at the inception, and again (to a lesser 

 extent) at an epoch corresponding to that of direct arrival 

 of transversal waves, it may be described, in general terms, 

 as consisting of a long undulation leading up to the main 

 shock, and dying out gradually after this has passed. 

 Its time-scale is more and more protracted, and its ampli- 

 tude more and more diminished, the greater the distance 

 from the source. The main shock, on the other hand, is 

 propagated as a solitary wave (with one maximum and one 

 minimum, in both the horizontal and vertical displace- 

 ments) ; its time-scale is constant, and its amplitude 

 diminishes only in accordance with the usual law of 

 annular divergence, so that its total energy, unlike that of 

 the minor tremor, is maintained undiminished. Its velocity 

 is that of free Rayleigh waves, and is accordingly somewhat 

 less than that of waves of transversal displacement in an 

 unlimited medium. 



" A Method for the Investigation of Fossils by Serial 

 Sections." By Prof. W. J. Solla*. F.R.S. 



Mechanical difficulties preclude the study of fossils by 

 serial thin slices, but serial polished surfaces may be 

 obtained at any desired degree of proximity, and these, when 

 the fossil and its matrix offer sufficient optical contrast, 

 serve most of the purposes of thin slices. They may be 

 photographed under the microscope, so as to furnish a trust- 

 worthy and permanent record. The sections may be used 



to obtain reconstructions of the fossil in wax. Several 

 fossils have been successfully studied in this way, such as 

 Palaeospondylus Gunni, Ophiura Egertoni, Lapworthura 

 Miltoni, Monograptus priodon, and Palaeodiscus ferox. 

 The sections are obtained at regular intervals, usually of 

 0025mm., by means of an apparatus designed for the 

 purpose by the Rev. F. Jervis-Smith, F.R.S., reader of 

 mechanics in the university. 



" An Account of the Devonian Fish, Palaeospondylus 

 Gunni, Traquair." By Prof, W. J. Sollas, F.R.S., and 

 Igerna B. J. Sollas. 



June 18. — " Some Preliminary Observations on the 

 Assimilation of Carbon Monoxide by Green Plants." By 

 Prof. W. B. Bottomley and Mr. Herbert Jackson. Com- 

 municated by Prof. J. Reynolds G.-een, F.R.S. 



" The Bionomics of Convoluta roscoffensis.'" By Dr. 

 F. W. Gamble and Frederick Keeble, M.A. 



Convoluta is a minute green Turbellarian organism that 

 lives in such prodigious numbers on the coast of Brittany 

 as to cover long stretches of the beach with a thick green 

 scum. 



Previous observers have directed attention to the fact 

 that Convoluta is not merely an animal, but is an associa- 

 tion of an animal and a plant, or plant-like organism, which 

 is represented by the green cells. These cells contain 

 chlorophyll, perform photosynthesis, and store starch, but, 

 unlike algal cells, they have no cell-wall, and they are 

 believed to have no power of surviving the death of the 

 animal tissue. Whether they are exceptional animal cells 

 or infecting plant-cells, or algae acquired in past time and 

 now inherited, is unknown. But it is supposed that the 

 life of the animal has been modified to suit their require- 

 ments, that from their reserves the animal is fed, and that 

 to the renewal of these reserves its movements are directed. 



The present paper is an attempt to gain further insight 

 into this strange problem. Dealing first with the question 

 of food, the authors show what rays of light are effective 

 in producing a surplus of starch, but they believe that this 

 reserve does not furnish the source of food on which the 

 animal tissue of Convoluta is nourished ; for not only does 

 this starch disappear with extreme slowness (7-8 days) in 

 darkness, but direct evidence is forthcoming that in all 

 stages of development Convoluta can, and does, ingest, that 

 in the earlier ones diatoms and algae are normally ingested 

 and digested, and that in the later stages the green cells 

 are bodily aggregated and digested in the gut. 



Passing to the development of the green cells, the authors 

 find the first trace of these cells as colourless, nucleated 

 structures in the gut of the recently hatched animal. Direct 

 proof of the intrinsic or extrinsic origin of these colourless 

 cells is still lacking. The indirect evidence, however, is 

 strongly in favour of the latter mode of origin. On this 

 view Convoluta makes a pure culture from a mixed in- 

 fection. 



Further analyses than heretofore of the effects of light, 

 heat, gravity, and other agencies on the behaviour of Convo- 

 luta are given. The tonic, even more than the tropic, effect 

 of light determines the periodic tidal movements, now to 

 the surface of the sand, and now below the surface. The 

 direct tropic effect of light is greatest in the green rays, 

 absent in the blue, and reversed in the red. The effect is 

 modified by the absorbing or scattering character of the 

 background, and by the age of the animal. At the moment 

 of hatching, Convoluta is aphototropic. 



Geotropic response is not exhibited by those Convoluta 

 which fail to develop their otolith. Normally it is shown 

 from the moment of birth. 



The paper concludes with a description of the daily and 

 lunar variations in the size and behaviour of the colonies, 

 and with an explanation of these variations in terms of the 

 tropisms and other habits of Convoluta. 



" The Spyectra of Neon, Krypton, and Xenon." By 

 E. C. C. Baly, Lecturer on Spectroscopy in University 

 College, London. 



The gases were illuminated by the passage of the dis- 

 charge from an induction coil through them under reduced 

 pressures. Vacuum tubes were filled with each one of 

 them, and the glowing gas in a capillary portion was ex- 

 amined " end on " through a quartz window. Considerable 

 difficulty was experienced in the use of the tubes, owing to 

 th? disintegration of the electrodes and the absorption of 



NO. 1758, VOL. 68] 



