March 12, 1896] 



NATURE 



445 



H^tricts ; and ultimately the whole would be generalised into one 

 icmoir on the whole country, the result of a series of generalisa- 

 iions carried out much in the same way as the various maps of 

 the Ordnance Survey are obtained by successive generalisations 

 from the largest scale produced. The chief sources of in- 

 rmation would be the topographical map of the Ordnance 

 arvey, the maps of the Geological Survey, the charts of the 

 Hydrographic Department, the publications of the Meteoro- 

 logical Office, the Census reports, the reports of the Board of 

 Trade and other Government departments, the publications of 

 such societies as the Royal Agricultural, the Archiiiological, the 

 Statistical, the Institution of Civil Engineers, and many others, 

 lul the pictures of amateur photographic societies. Dr. Mill 

 plained in detail the plan of the proposed memoir, and the 

 method in which it should be carried out. After a discussion, 

 Mr. Clements Markham, who occupied the chair, said he should 

 certainly recommend to the Council that the memoir be prepared 

 under the Society's auspices. The practical problem of expense 

 has, however, to be solved before the plan can he developed. 



An important contribution to the knowledge of the origin 

 and movement of sand, shingle, and alluvial matter around 

 our coasts, was made by Mr. W. H. Wheeler at the meeting 

 of the Institution of Civil Engineers last week. It appears 

 that the generally accepted theory, that the travel of drift 

 along a coast is due to and is in the direction of the prevail- 

 ing wind, is contrary to fact. In England the prevailing winds 

 : e from the south-west ; whereas the travel of drift on the east 

 Miist is southward, on the south coast from the westward, and 

 on the west coast northward, in each case being in the same 

 direction as the flood tide. Mr. Wheeler has been unable to 

 find a single instance where the regular and continuous travel of 

 drift along a coast is in the opposite direction to that of the 

 flood tide. While winds and waves are the agents which 

 operate in eroding cliffs and producing the supply of drift, the 

 continuous progressive movement of sand and shingle along the 

 sea coast is caused by the wave action of the flood tide, which is 

 increased when the wind blows in the same direction as the flood 

 tide. With regard to alluvial matter in estuaries, this is derived 

 from detritus brought down by rivers, and does not come from 

 the sea, nor is it supplied from the waste of clay or chalk cliffs 

 along the sea coast. The only current along the coasts of 

 England which can transport material in suspension is that due 

 to the tidal wave, which travels each way for about six hours at 

 the rate of between 2 knots and i\ knots. It is known that the 

 material in suspension is not carried upwards for any great 

 distance above the mouth of a river or estuary. The tidal wave 

 propagated up a river creates only an oscillating current, and the 

 same quantity of tidal water which goes up returns on the ebb, 

 with the addition of the current produced by the fresh water ; 

 the tendency of movement is, therefore, downward, and not 

 upward. Mr. Wheeler applied these and other facts to deter- 

 mining the principles which are essential in the construction 

 I A harbours on shingly or sandy coasts. 



The current number of the Coniptes rendits (March 2) 

 mains a pap)er by M. Henri Becquerel, on some invisible 

 nliation emitted bv phosphorescent bodies. In some previous 

 experiments the author has shown that phosphorescent bodies 

 :4ive out radiation which i.- capable of traversing bodies which 

 re opaque to ordinary light rays. The great interest at present 

 "wn in this subject has induced him to give an account of 

 numl>er of recent experiments. The phosphorescent bodies 

 1 1 ployed have Ijeeti crystals of the double sulphate of uranium and 

 tassium. The phosphorescence of this body is very marked, 

 I ait only lasts, as far as the rays which affect the eye are con- 

 cerned, at any rate, for less than one-hundredth of a second. It 

 can easily be shown that the rays emitted by this body when 

 NO. 1376, VOL. 53] 



exposed to diffused daylight or to direct sunlight are capable of 

 traversing not only black paper, but also aluminium and thin 

 sheets of copper. For if an ordinary dry photographic plate, 

 enclosed in a tin-plate slide with an aluminium window, is 

 exposed to sunlight even for a whole day, the plate is unaffected. 

 If, however, a crystal of the uranium salt is placed on the 

 aluminium window, and the whole is exposed to sunlight for a 

 few hours, then on developing the plate a shadow of the crystal 

 will appear in black. If a thin plate of copper, cut into the form 

 of a cross, is placed between the crystal and the aluminium 

 window, a clear image of this cross is formed on the plate. The 

 curious result has, however, been obtained that although the 

 plate-holder and the uranium salt are not exposed to the light, 

 but kept inside a wooden or cardboard box, the photographic 

 plate shows the same images as when the salt is exposed to 

 light. The author rather tentatively suggests that the uranium 

 salt may continue to emit by phosphorescence radiation that is 

 invisible to the eye, but which is capable of traversing paper and 

 aluminium for a time infinitely great compared with the time 

 during which it continues to emit visible rays. 



The February number of the Journal de Physique contains a 

 paper, by M. C. Limb, on the determination of the electromotive 

 force of a Clark cell in absolute measure. Instead of adopting 

 the usual method, which is to compare the difference of potential 

 at the ends of a known resistance when traversed by a known 

 current with that of the cell, the author has adopted a novel 

 method whieh is independent of the units of current and resist- 

 ance. A magnet is rotated inside a long helix about an axis 

 perpendicular both to its own magnetic axis and the axis of the 

 coil. The magnetic moment of the magnet is determined by 

 Gauss's method. If H is the field which would be produced at 

 the centre of the long coil if the spirals were traversed by unit 

 current, at the angular velocity of the magnet and M its magnetic 

 moment, then the maximum value of the electromotive force 

 induced in the coil will be HMw. A correction has to be 

 applied on account of the finite length of the coil which involves 

 the distance between the poles of the magnet. The angular 

 velocity is measured by simultaneously registering the turns 

 made by the magnet and the beats of a seconds pendulum, the 

 velocity being maintained constant by a specially designed 

 tachyometer. By means of a commutator fixed to the axle of 

 the magnet, the circuit of the coil is only closed at the moment 

 when the induced electromotive force is a maximum. This 

 maximum electromotive force is compared with that of the cell 

 by means of a modified form of Clark potentiometer, a 

 Lippmann capillary electrometer being employed to indicate 

 when the balance is secured. This electrometer is capable of 

 indicating a difference of potential of o*oooo5 volt. The Clark 

 cell was of the H pattern, and the author gives as his final 

 result for the electromotive force of this form of cell at 0° C. the 

 number i'4535- The number obtained by Lord Rayleigh was 

 I -4527 volts. 



The habit of opium-smoking forms the subject of a paper, by 

 M. H. Moissan, in the Annales de Chimie et Physique. M. 

 Moissan finds that the Chinese do not smoke crude opium, but a 

 preparation of it called Chatidu, which, when heated to about 

 250° produces a smoke formed of volatile perfumes and a small 

 quantity of morphine ; this appears to produce no more ill- 

 effects than tobacco-smoking. The commercial quality of 

 opium, however, is very different ; the residues that remain 

 after opium-smoking are sold as dross, and when this is treated 

 to a temperature of 300° to 325° various toxic compounds are 

 given off. 



We have received, from Mr. E. Kayser, a pamphlet contain- 

 ing a considerable number of measurements of cloud-heights 

 taken at Dantzig last summer. The observations were taken 



