February 8, 1894] 



'NA TURE 



355 



light on a minute pinhole, and placing the object between 

 the hole and a microscope eyepiece. Beyond the eye- 

 piece the camera used for photographing the pheno- 

 mena was placed. Permanent records of remarliably good 

 diffraction figures were obtained in this way, both of the 

 combinations of circles above mentioned and of various other 

 objects and geometrical forms. After showing geometrically 

 that diffraction bands from narrow obstacles and openings were 

 wider than those from broader ones, the author explained the con- 

 ditions necessary for making the bands visible, and pointed out 

 the distinction between internal and external bands. Promi- 

 nent amongst the photographs were several showing " Arago's 

 white spot" at the middle of a shadow, and, in particular, this 

 well-known phenomenon was shown as produced by so large an 

 object as a threepenny-piece. Speaking of diffraction in a 

 microscope, the author said little doubt need exist as to whether 

 an image represented the real object or a diffraction modification 

 thereof, for the latter were usually of a more misty and compli- 

 cated character. Departing somewhat from the subject of 

 diffraction, an excellent photograph of conically refracted 

 pencils was shown, consisting of circular lines of light produced 

 by passing light from pinholes through a crystal of arragonite 

 Dr. Johnstone Stoney thought the obtaining of permanent 

 records of diffraction phenomena of great importance, and was 

 particularly interested in the photograph showing conical 

 refraction. Prof. S. P. Thompson said he had never seen dif- 

 fraction effects exhibited to an audience so well before. He 

 had noticed that in several of the photographs Arago's spot was 

 unintentionally shown to perfection in the shadow of dust par- 

 ticles. The President greatly appreciated the fact that the 

 conical refraction photograph had been exhibited for the first 

 time before the Physical Society. — A note on a new photo- 

 metric method and a photometer for same, was read by Mr. J. 

 B. Spurge. The method consists in using two diffusing screens 

 (illuminated respectively by the lights to be compared) as second- 

 ary sources, and adjusting to equality the luminosity of equi- 

 distant internal surfaces by varying the apertures through which 

 the light passes from the screens to those surfaces. By reducing 

 the sizes of the apertures the author has been enabled to compare 

 lights of different colour, for when of sufficiently feeble intensity 

 coloured lights are indistinguishable from white or grey. The 

 photometer is made up of two tubes mounted at 45° to an axis, 

 about which one of them is capable of rotating. When in the 

 same horizontal plane, the axes of the tubes form the sides of an 

 isosceles right-angled tr angle, at the middle of whose hypothe- 

 nuse the light to be tested is place i ; this illuminates one of 

 the screens, whilst the standard light shines on the other. 

 These screens, used as secondary sources, are situated a short dis- 

 tance away from the outer ends of the tubes, whilst the inner sur- 

 faces of the near ends of the tubes are viewed by means of a mirror. 

 By turning the movable tube about the inclined axis, and rotat- 

 ing the source about a vertical axis, the illuminating effect of the 

 source in any direction can be tested. Capt. Abney saidthe law of 

 inverse squares was not true for weak lights, for the proportions in 

 which the light from sources of equal intensity had to be reduced 

 to appear white or grey depended greatly on the colour ; being 

 much greater for violet than for red. Only for the yellow-green 

 rays was the ordinary law of illumination true when the intensi- 

 ties were feeble. Mr. Blakesley, Prof. S. P. Thompson, and 

 the President also took part in the discussion. 



Geological Society, January 24. — W. H. Hudleston, 

 F.R.S., President, in the chair. — The ossiferous fissures in the 

 valley of the Shode, near Ightham, Kent, by W. J. Lewis 

 Abbott. The fissures occur in a promontory of Kentish Rag 

 between two tributaries of the Shode. There are four fissures 

 in this promontory, striking at right angles to the valley. Details 

 of the physiography of the area in which the fissures occur are 

 given in the paper. Three of the fissures have obviously been 

 in contact with the surface, and from these the bones appear to 

 have been dissolved out. The fourth does not reach the top of 

 the Rag, and further is sealed by an arragonite-lined chamber with 

 stalactitic floor and ceiling. This fissure is from 2 to 6 feet wide 

 and about So feet deep, and is filled with a heterogeneous col- 

 lection such as constitutes the flotsam and jetsam of streams, 

 along with materials derived from the rock in which the fissures 

 occur. Several thousand bones were found, also twelve species 

 of aquatic and land shells, an entomostracan, Chara and other 

 vegetable remains have been procured. The author gave reasons 

 for concluding that the fissures have never been reopened since 

 I hey were first closed by the materials introduced into them by 



NO. 1267, VOL. 49] 



the river, and that all the contained fossils belong to one and 

 the same geological period. He pointed to the discovery of 

 species not before found in Pleistocene beds as only a repetition 

 of what has occurred in other sections he had worked, aud 

 remarked also that the increase of species was corroborative of 

 a suggestion of Mr. C. Reid that the more we discover of the 

 smaller creatures of this and the preceding age, the more they 

 approximate to those of our own times. Even if we iwere to 

 exclude from the lists all the species not previously found fossil 

 elsewhere, we still have an extensive assemblage of the older 

 Pleistocene forms, which must have lived during the filling of 

 the fissures, and this therefore fixes the filling operation as having 

 occurred in Pleistocene times.— The vertebrate fauna collected 

 by Mr. Lewis Abbott from the fissure near Ightham, Kent, by 

 E. T. Newton, F. R.S. The vertebrate remains collected by 

 Mr. Lewis Abbott have been passed in review by Mr. Newton, 

 and as far as possible specifically identified : they represent 

 mammals, birds, reptiles, and amphibians ; but no fishes have 

 been found. In all, 48 different forms have been recognised ; 

 3 or perhaps 4 are extinct ; 11 are extinct in Britain, but are 

 still living elsewhere ; 21 are living in Britain, but are known to 

 be Pleistocene or forest-bed forms ; and 12 are species now 

 living in Britain which have not hitherto been recognised in 

 Pleistocene or older deposits. Among the more important 

 species found in this fissure, but extinct in Britain, may be 

 noticed, besides Elephas primigenitis. Rhinoceros antiqiiiiatis, 

 and Hyana, the Ursus arcios, Canis lagopiis, Myodes torqiiattcs, 

 Myodes lemtnus, Microtus gregalis, M. ratticeps, Lagomys 

 pusillus, Spennophihis, and Cerviis tarandus. The name of 

 Mttstela robusta was proposed for some limb-bones intermediate 

 between the polecat and marten, and the remains of an extremely 

 small weasel are noticed as a variety of Miistela vulgaris. 

 Although the large number of living species gives a recent 

 aspect to this series of remains, the evidence, it is believed, 

 points rather to their being all of Pleistocene age, and most 

 nearly allied to the fauna of British caves. In the course 

 of some remarks upon the paper, Mr. Topley compared the 

 fissures filled with loam and gravel, and containing mammalian 

 bones and land-shells, of the Maidstone district with the interest- 

 ing example described, and explained that those of the Maid- 

 stone Rag country were connected with overlying deposits of 

 drift, the material now filling the fissures having been let down 

 into the rock by solution of the limestone along joints and 

 cracks. Sir Henry Howorth and Dr. Henry Hicks also spoke, 

 and Mr. E. T. Newton briefly replied. 



Paris. 



Academy ot Sciences, January 29. — M. Lcewy in the 

 chair. — An account of the work of A. Scacchi, by M. Des 

 Cloizeaux. — Integration of the equation of sound for an in- 

 definite fluid in one, two, or three dimensions, when there are 

 different resistances to the movement ; physical consequences of 

 this integration, by M. J. Boussinesq. — On the propagation of 

 an electric current in a particular case, by M. A. Potier, — • 

 Anomalies in the force of gravity observed on the North 

 American Continent, by M. Deftorges, The value of g 

 for a number of stations between VVashington and San Fran- 

 cisco is as follows: — -Washington 9So"i67, Montreal 980729, 

 Chicago 98o'345, Denver 979 '684, Salt Lake City 979'8i6, 

 Mt. Hamilton 979'683, and San Francisco 98o'oi6. These 

 values, reduced to sea-level and compared with the theoretical 

 values calculated from Clairaut's law, show regular anomalies 

 which are compared with anomalies exhibited by oceanic 

 islands. — Theory of the elasticity of metals, by M. Felix Lucas. 

 — On the new measurement of the area of France, by General 

 Derrecagaix. A planimeter measurement, calculated on the 

 assumption that the figure of the earth is a true ellipsoid of 

 revolution. Supplementary remarks were made by M. E. 

 Levasseur. — On the rapid summation of certain slightly con- 

 vergent series (alternate harmonic series), by M. A. Janet. — 

 On a common property of three particular classes of rectilinear 

 congruences, by M. Alphonse Demoulin. — Joule's and Mar- 

 riotte's laws in connection with existing gases, by M. Jules 

 Andrade. The author shows that these laws are true for real 

 gases within about the samelimitsof accuracy. — An electric alarm 

 thermometer for laboratory ovens, by M. Barille. Connection 

 of an electric circuit is made when the mercury in the thermo- 

 meter reaches a determined point on the scale by means of a 

 platinum wire which is attached to a small iron tube (sliding 

 along a fixed wire), of which the position can be regulated Q'j a 



