66 



NATURE 



{May 1 6, 1889 



Results of experimenls with working model of the tidal Seine, 

 exhibited by Mr. L. F. Vernon Harcourt. These experiments 

 were undertaken with the object of obtaining an indication of 

 the effects which the various schemes proposed for the improve- 

 ment of the estuary of the Seine, by the prolongation of the 

 training walls below Berville, would have upon the estuary 

 if carried out. After ascertaining, by experiments, that the 

 former and present conditions of the Seine estuary could be 

 reproduced in miniature in the model, the various schemes 

 proposed were successively introduced in the model, with the 

 results shown upon the diagrams exhibited. The method of 

 working this model has since been applied to the model of 

 another estuary, which may be seen in operation at 6 Queen 

 Anne's Gate, Westminster. 



Profs. A. W. Riicker, F.R.S., and T. E. Thorpe, F.R.S , 

 exhibited maps to illustrate the direction and magnitude of the 

 regional magnetic disturbing forces in the Briti h Isles. The 

 British Isles can be divided into a comparatively small number 

 of districts, in each of which the horizontal disturbing forces 

 tend towards centres or loci of attraction, which are also regions 

 of large vertical force. The shaded portions of the maps are 

 districts of high vertical force, and it will be seen that the 

 arrows which represent the horizontal forces on the whole point 

 towards them. In Scotland the forces indicated by tlie do'ted 

 arrows were deduced from data collected in 1857-58 by Mr, 

 Welsh. The five principal lines towards which the magnetic 

 disturbing forces in Great Britain converge aie in the immediate 

 neighbourhood of (i) the Caledonian Canal ; (2) the basalt of 

 the Western Isles ; (3) the centre of the Scotch coal-field, in 

 which basaltic crystalline rocks occur ; (4) the line in South- 

 East Yorkshire, in which the Jurassic and Liassic strata thin 

 out, and passing thence to the Lakes ; (5) the Palaeozoic ridge 

 between London and the South Wales coal-field. There are 

 well-marked centres of attraction, (i) between Reading and 

 Windsor, (2) near the Wash, which have been specially studied. 

 The disturbance which culminates in the first extends from 

 Kenilworth to the Channel, and from Salisbury to the North 

 Sea. The well-known anomaly in the difference of the declina- 

 tions at Greenwich and Kew is thus accounted for. The maps 

 also afford indications of other subsidiary centres. 



Captain H. Capel L. Holden, R. A., showed : — (i) Chrono- 

 graph for measuring the velocity of projectiles and small periods 

 of time. This chronograph, of which the latest form with 

 Captain Holden's most recent improvements is exhibited, is of 

 the gravity type, originally invented by M. Le Boulenge ; since 

 its first introduction it has been improved by Captain Breger, 

 of the French Marine Artillery. Broadly speaking, it consists 

 of a heavy pillar, to which are affixed two electro-magnets (the 

 circuits of which are arranged to be interrupted by the action of 

 the body whose velocity it is required to measure) which can 

 support two rods, the shorter one of which, in falling, strikes a 

 trigger table and releases a knife, which marks the other as it 

 falls. The time elapsing from the commencement of the fall of 

 the short rod until the knife strikes the other rod is obtained 

 mechanically by means'of the instrument called the disjunctor, 

 which breaks both of the separate circuits simultaneously : a 

 commutator in connection with this disjunctor enables errors 

 due to the circuits not being broken simultaneously to be de- 

 tected and corrected for. When an interval of time occurs 

 between the two circuits being broken, the mark made on the 

 rod by the knife will be more or less above that made when the | 

 disjunctor is used, and the space between the two marks gives | 

 the means of ascertaining the time, since the rod falls under the i 

 influence of gravity. In ordinary use, the screens, where the 

 interruption of the circuit takes place, are made of a continuous 

 wire in circuit, each with its electromagnet and battery, and these 

 screens are broken by the passage of the projectile through them. 

 The disjunctor reading is arranged i-o as to be adjustable by 

 altering the height of the magnet, so that, the screens being a 

 fixed distance apart, a scale can be engraved on the micrometer 

 bar of velocities in feet per second, thus saving time and avoid- 

 ing frequent calculation. — (2) Holden hydrometer. This is 

 intended more especially for use in connection with secondary 

 batteries, for observing the density of the acid during charge 

 and discharge. It consists of two parts — the hydrometer- float 

 and the scale. In use, the scale is clipped to the battery plates 

 or to the side of the containing vessel, the point being pushed 

 down until it just touches the liquid, and the reading is then 

 taken from the top of the hydrometer stem on the ebonite scale. 

 The range of density and the size of the divisions can be varied 



according to the requirements. The advantages claimed for this 

 form over the ordinary type of hydrometer are : greater sen- 

 sitiveness, more open scale, and increased legibility owing to the 

 reading being above the level of the liquid and side of the cell, 

 freedom from adherence to the plates or side of the vessel, and 

 the ready correction for temperature by means of a sliding scale. 



A model illustrating the formation of ocean currents, exhibited 

 by Mr. A. W. Clayden. This is practically a map of the 

 Atlantic in which the land surfaces are raised about half an inch 

 above the portions occupied by the sea. The continents and 

 larger islands are made of wood cut into the required shape, 

 while the smaller islands are represented by pins or small pieces 

 of sheet metal driven into the board which forms the basis of the 

 whole. This raised map forms the bottom of a shallow tray 

 which can be filled with water up to the level of the land sur- 

 faces, thereby obtaining a map (on Mercator's projection) in 

 which the seas are represented by the surface of water. Under- 

 neath the tray a wind chest is fixed, and a number of tubes are 

 brought up from it through the continents, and bent over so that 

 the jets of air delivered from them may impinge upon the water. 

 These jets are so arranged as to approximately reproduce on a 

 small scale the actual circulation of the atmosphere as laid down 

 on a chart of the prevalent winds for the year. Care is taken to 

 have as few tubes as possible, and they are so placed as to hide 

 the least possible amount of the sea. The strong and persistent 

 trades are simulated by bringing the openings of the tubes near 

 to the surface of the water, while the fitful and uncertain winds, 

 of northern latitudes are imitated by allowing the jet to be con- 

 siderably dis|.ersed before coming into contact with the water. 

 A foot-blower is attached to supply the wind, and any movement 

 of the water is rendered visible by scattering over it some 

 Lycopodium powder. A few moments after the blast is turned 

 on, the whole surface of the model sea is in motion. All the 

 principal currents of the North Atlaiitic are shown, including the 

 return current between the great equatorial currents, and the 

 northward stream along the west coast of Greenland. If a 

 narrow opening is made in the Isthmus of Panama all that 

 happens is that some of the return stream round the Mosquito 

 Bay and Gulf of Parien flows into the Pacific, leaving the North 

 Atlantic practically unaffected. But if a large part of Central 

 America is removed, almost the whole of the tropical water passes 

 through the opening, and the currents from Baffin's Bay and the 

 Arctic Ocean are drawn down to the Azores and the Canary 

 Isles. There is an absence of evident connection between the 

 slack water close to the New England coasts and the Labrador 

 current, but the apparatus does not attenr.pt to imitate differences 

 of temperature or differences of rotational velocity, hence any 

 effect due to either of those causes must necessarily be absent. 

 All that is attempted is to demonstrate the connection between 

 the prevalent winds and general oceanic circulation, by showing 

 that nearly all the movements of the water are determined by the 

 direction of the winds and the contours of the coasts. 



Mr. James Pitkin exhibited :— (i) Pitkin and Niblelt's fire- 

 damp meter. By means of these instruments it is possible to 

 detect and estimate the percentage of oxygen or hydrogen in 

 mixtures of these gases. In its simplest form it consists of two 

 ordinary cylindrical bulbed mercurial thermometers. These are 

 mounted on a suitable base, and are then graduated off in the ordi- 

 nary v/ay to Fahrenheit or Centigrade scale. One tube registers 

 the temperature of the mixed gases. The other, which is the gas 

 indicator, has its bulb coated with one of those metals which 

 when in a very finely divided state have the peculiar property of 

 occluding and facilitating the chemical combination of certain 

 gases. When placed in a gaseous mixture and during the 

 combination of the gases due to the above property of the metal, a 

 considerable amount of heat is developed. The heat generated 

 thus produces a corresponding rise in the mercurial column. To 

 read the instrument the difference between the two scale readings 

 is taken, and then, by comparison with a table supplied with each 

 instrument, the percentage of gas may be read off. In the case 

 of fire-damp and air or coal-gas and air, the amount of heat 

 developed appears to correspond approximately to the explosive 

 activity of the mixed gases. A sliding scale may be fixed on the 

 instrument, which can be graduated in terms of percentages of 

 any particular gas. — (2) Pocket electric lamp. This lamp is 

 constructed for astronomical and other scientific purposes where 

 a steady and a safe light is occasionally required. Its total 

 weight is i lb. 13 oz., and it gives a light of i candle-power for- 

 a period of six hours. Its charging current is i ampere at a 

 potential of 5 volts for four hours. 



