May 2 2, 1890] 



NATURE. 



95 



on the unstrained bar will remain horizontal and straight on the 

 strained bar. An element at Q, however, will be subjected to 

 unequal strains, for EF is < GH, hence the lower points of the 

 elements will be displaced towards the axis. This displacement 

 will increase as the distance beyond d and c from the axis in- 

 creases, and an originally horizontal line will become curved at 

 the ends cd and ef, whilst de will remain straight. In a similar 

 way it was shown that horizontal lines should assume the shapes 

 indicated at ghi, jklmn, opq, rst, and uv, in their respective 

 positions, whilst vertical lines should become pinched inwards 

 above and below the shoulder as shown by the curve li'xxfyz. 

 To test whether the reasoning, by which the above conclusions 

 were arrived at, was satisfactory, a copper bar was carefully pre- 

 pared, ruled, and subjected to permanent strain. The curvatures 

 of the various lines clearly show the characteristics predicted by 

 theory. Prof. Perry inquired whether it was correct to assume 

 the stress uniform over the plane sections inclined at 45" to the 

 axis. He also said that the general character of the flow some- 

 what resembled that of a viscous fluid passing from a wide to a 

 narrower channel. Prof. Herschel thought Mr. Carus-Wilson 

 justified in assuming the stress uniform over the diagonal sec- 

 tions ; the latter said he only made the assumption as a pro- 

 visional hypothesis, but the results of his experiment agreed so 

 closely with his theoretical deductions that he thought the hypo- 

 thesis correct. — Mr. C. V. Boys made two communications, (i) on 

 photographs of rapidly moving objects, and (2) on the oscillating 

 electric spark. A collection of apparatus by which he had been 

 able to photograph drops of water in their various stages of 

 formation was exhibited. It consisted of a lantern and lenses by 

 which a trough in which the drops were formed could be strongly 

 illuminated, combined with a camera and revolving disk with one 

 perforation. By th.'s means exposures of about 1/600 of a 

 second could be made about 20 times a second. The slide of the 

 camera was about 3 feet long, and could be moved across the 

 field by hand so as to take the consecutive impressions on different 

 parts of the plate. The resulting photographs show with re- 

 markable clearness the formation, breaking away, the oscillations 

 of the drops, and their rebounding in the liquid into which they 

 fall. By cutting the photographs into strips, each strip re- 

 presenting a single exposure, and mounting them on a disk, Mr. 

 Boys had arranged a kind of thaumatrope which represented the 

 phenomena in a very realistic manner. He also exhibited photo- 

 i;raphs of small water fountains broken up into drops by musical 

 sounds, which he had taken by the electric spark without the aid 

 of lenses. The shadows of the drops were sharply defined even 

 when magnified considerably, and the various stages of transition 

 from the liquid column to the detached particles were well 

 shown. Finding it possible to obtain such good results from a 

 simple spark, it occurred to him that he might get a succession 

 of photographs from the intermittent light of an oscillating 

 spark, and in this he was fairly successful. An apparatus devised 

 to show the oscillatory character of a discharge was next ex- 

 hibited in operation. It consisted of a disk carrying six lenses 

 arranged in two sets of three. The members of each set were 

 at different distances from the axis so that the images of the 

 spark on the screen do not coincide. The disk can be revolved 

 at a high speed, and the successive sparks are seen as bright 

 patches on the screen. By this apparatus a single discharge can 

 be examined, whereas with Dr. Lodge's apparatus it is desirable 

 to have a fairly rapid succession of sparks. Photographs of an 

 oscillatory discharge taken with the apparatus were exhibited, 

 and these show that the duration of the illumination is a con- 

 siderable fraction of a complete period. Lord Rayleigh said he 

 was greatly interested by Mr. Boys's apparatus. He (Lord 

 Rayleigh) had photographed water fountains both when broken 

 up, and when made to coalesce under electrical influence, but it 

 had never occurred to him that it would be possible to get 

 enough light or sufficient sharpness from a single spark. Mr. 

 Boys s success he believed to be owing to the fact of his using no 

 lenses, which would absorb the ultra-violet rays. He also 

 thought the method might be developed so as to give shaded 

 pictures instead of mere representations in black and white. 

 Mr. Gregory asked Mr. Boys if he had tried to get greater 

 potentials for his oscillatory discharges by using Dr. Lodge's 

 " impulsive rush " arrangement. Mr. Trotter inquired whether 

 the single sparks used to photograph the water fountains were 

 as large as those required to show oscillations. Mr. Boys said 

 he had not tried Dr. Lodge's "impulsive rush" arrangement 

 because of the enormous capacity of the condensers required. 

 The sparks used to photograph the broken up fountain were very 



NO. 1073, VOL. 42] 



small, being only about \ inch long, and from a few jars. Prof. 

 Perry asked Lord Rayleigh whether it would be possible to 

 compare the shapes of the water drops shown in the photographs 

 with the shapes of the liquid surfaces of revolution given by 

 Sir William Thomson at the Royal Institution some years ago, 

 or whether the changes of shape were too rapid to permit of the 

 surface tension being all important. Mr. Boys thought the 

 motions of the drops would be too rapid, and that inertia would 

 play an important part. Lord Rayleigh pointed out that by 

 forming a drop slow enough the effect of inertia might be made 

 negligible until such time as the unstable state was reached ; 

 after that, however, inertia must have considerable influence on 

 the shape. 



Geological Society, April 30.— Dr. A. Geikie, F.R.S., 

 President, in the chair. — The following communications were 

 read : — On certain physical peculiarities exhibited by the so- 

 called "raised beaches" of Hope's Nose and the Thatcher 

 Rock, Devon, by D, Pidgeon.— The Devonian rocks of South 

 Devon, by W. A. E. Ussher, of H.M. Geological Survey. This 

 paper is the result of work done in continuation of the labours 

 of the late Mr. Champernowne, and refers particularly to the 

 area north of the Dart and east of Dartmoor. Owing to the 

 complicated stratigraphy of the region, we have to fall back 

 upon such information as can be procured of the general types of 

 Upper, Middle, and Lower Devonian faunas ; for though the 

 lithological constituents of these three divisions are broadly 

 distinguishable, there are no definite lithological boundaries 

 between them. The Lower Devonian is mainly distinguished 

 by the occurrence of sandstone and grit, but the upp^r beds are 

 shales passing into the Middle Devonian slates. 1 he Middle 

 Devonian consists of limestones, and shaly limestones upon 

 slates, the latter representing the Calceolen-Schiefer, and con- 

 taining Spinifer speciosus. Stringocrphalus is found here and 

 there in the middle Devonian Limestones. The upper part of 

 the middle Devonian Limestones (with Lummaton fauna) passes 

 into the Cuboides beds of the Upper Devonian. The Upper 

 Devonian contains thin- bedded limestones, often concretionary, 

 with chocolate-red and pale greenish slates and mudstones. 

 These beds correspond to the Goniatiten-Schichten, Kramenzel- 

 stein and Knollenkalk of Germany, and to the Cypridinen- 

 Schiefer. In the Upper and Middle Devonian rocks we find a 

 local prevalence of schalstein and tuffs, breaking up the lime- 

 stones. The slate and sandstone type of Upper Devonian in 

 North Devon appears to give place southward to a purely slate 

 type, possibly accompanied by overlap of the Culm measures. 

 The author groups the South Devon rocks under the following 

 heads : — 



Upper. 



Middle. 



Lower. 



f 3- 



Cy pridinen - Schiefer. 



Goniatite- limestones and slates. 



Massive Limestones. 



Ashprington Volcanic Series. 



Middle Devonian Limestones. 



Eifelian slates and shaly limestone. 



Slates and sandstones, generally red. 



Slates with hard grits. 

 After discussing the relationship of the Lincombe and Warberrj- 

 beds and the New Cut Homalonotus beds, the author notes the 

 discovery of Pleurodictynm by Mr. Whidborne in the railway 

 cutting at Saltern Cove. He proves the Lower Devonian age 

 of the Cockington beds and their correlation with the Torquay 

 Lower Devonian by the discovery of fossils. He considers it 

 probable, though not certain, that the main mass of Meadfoot 

 beds is below the Lincombe, Warberry, and Cockington sand- 

 stones. The distribution of the Middle Devonian Limestones is 

 described. Stringocephalus is found in limestones containing 

 Rhynchonella cuboides. The upper parts of the limestone-masses 

 (East Ogwell, Kingskerswell, Barton, Ilsham, &c.) may be 

 Upper Devonian. The massive limestones may terminate 

 abruptly or pass laterally into shales, and the whole mass of 

 the limestones seems to be replaced by slates between the 

 Yealmpton and Totnes areas. The commencement of the phase 

 of volcanic activity which caused the accumulation of the Ash- 

 prington series is shown to coincide with the latest stage of 

 Eifelian deposition, and the Ashprington scries may represent 

 continuous or intermittent vulcanicity up to a late stage in the 

 Upper Devonian. North of Stoke Gabriel a mass of limestone 

 seems to have been formed contemporaneously with the volcanic 

 material on the immediate borders of which it occurs. Else- 

 where the limestones are interrupted by local influxes of volcanic 



