Oct. 24, 1889] 



NATURE 



dx I 



of constant quantity, a closed metallic circuit of which travelling 

 motors at all times form a part without ever being short-circuited, 

 or having the current supply cut off from them, and the regula- 

 tion of the power developed by the motor and absorbed by it 

 without interrupting the continuity of the circuit. An insulated 

 cable connected to one terminal of the generator traverses the 

 whole length of the line, and is interrupted at distances of 

 ' .20 feet, the divided ends being connected with the opposite 

 " faces of a "spring jack," which is at the same time the auto- 

 matic switch and contact point. The current collector, which is 

 the same length as and carried by the car, is constructed so as 

 to pass between the faces of the " spring jack," and conduct the 

 current to the motor without at any time short-circuiting it or 

 interrupting the main circuit. In series running, there is little 

 danger of damage to the motor by careless driving, or reversing 

 while running ; in descending a gradient there is positive advan- 

 tage in checking the speed of the car by altering the field con- 

 nections, so that the armature tends to revolve in the opposite 

 direction to that in which the car is travelling ; the power that 

 would otherwise be lost in braking is thus added to that produced 

 by the generator. 



Telephonic communication between London and Paris, by Mr. 

 W. H. Preece, F.K.S. The difficulty of such a communication 

 was not the distance, 275 miles, between the two towns, as in 

 the United States speech is maintained between New York and 

 Boston, 350 miles apart ; but the insertion of underground 

 wires at each end, and of a cable in the middle, places diffi- 

 culties in the way that have to be surmounted. The author has 

 experimented on the cables between Dover and Calais and others, 

 and finds the conditions to be fulfilled simple. The circuit must be 

 metallic, the material copper, and the product of the resistance 

 of the line and its capacity must not exceed 7500 for very good, 

 5000 for excellent, and 2500 for perfect speech. A circuit 

 approaching as nearly as possible one between London and 

 Paris was made on an artificial cable, and found to comply with 

 the requirements. 



On the purification of sewage and water contaminated with 

 organic matter by electrolysis, by Mr. W. Webster. The paper 

 was divided into four sections, of which the fourth referred to 

 the use of the electric current. The fact that water and the 

 salts contained therein are easily decomposed if the current is 

 of sufficient intensity is the explanation of the whole system. 

 The changes taking place in sewage when electrolyzed depend 

 chiefly on the splitting up into their constituent parts of sodium, 

 magnesium, and other chlorides, nascent chlorine and oxygen 

 being set free at the positive and the bases at the negative 

 pole. 



The strength of alloys at different temperatures by Prof. 

 W. C. Unwin, F.K.S. In 1877, the Admiralty made some ex- 

 periments as to the effect of variation of temperature on the 

 tenacity of copper, Muntz metal, and phosphor bronze, and 

 found that up to 500° F. the tenacity diminished propor- 

 tionately with increase of temperature ; in the case of gun metal, 

 on the other hand, the tenacity diminished regularly up to 300° 

 to 350°, but beyond this temperature there was a sudden 

 reduction in the strength, which was found to be as low 

 as half that at ordinary atmospheric temperature, whilst at 

 500° it became nil: the gun metal tested consisted of alloys 

 of copper, tin, and zinc combined in different proportions. 

 The author determined to make a series of experiments, the 

 results of which he brought before the Association. The various 

 alloys used, which are tabulated below, were heated in an oil 

 bath, the temperatures employed, being all below that of the 

 boiling of mercury, were read by means of a mercury thermo- 

 meter. The results were plotted on a diagram, and given in 

 tables, and show that the decrease of tenacity follows a regular 

 law in each case ; the temperature was given in degrees Fahren- 

 heit, and the tenacity in tons on the square inch. 



Gun Phosphor 



metal. bronze. 



1 1 '66 i6'o6 



ii'o6 i2'30 



7'84 ii"ii 



1715(615°) 4'8a(6oo") 817 



The influence of variation of temperature on the ductility of 

 the same alloys was also experimented on, and was found to 

 vary with the different alloys ; with brass and gun metal there 

 was little elongation before fracture ; with Muntz metal it was 

 considerable. In these cases the ultimate elongation diminished 

 with increase of temperature, but in the case of Delta metal it \ 



increased. These experiments are of a very important character, 

 and were carried out by the author on account of the very high 

 pressures, and therefore temperatures, at which modern steam- 

 engines are worked. 



Central station heating and power supply, by Mr. W. W. 

 Phipson. The system consists in the constant circulation of 

 water at high temperature and pressure (viz. 400° F. and 250 

 pounds per square inch) from boilers at the supply station, 

 through supply mains covered with non-conducting material, 

 and back to the boilers by means of return mains, the circula- 

 tion being maintained by pumps. Service boxes to supply the 

 houses are fixed under the footpaths, which are connected to 

 the mains by an inch pipe. From these boxes the house supply 

 is taken by means of copper pipes. A vessel, called a con- 

 verter, is fixed inside the house, whose use is to permit the 

 water to resolve itself into steam, the pressure of which is con- 

 trolled by means of a reducing-valve fixed on the copper pipe, 

 before it enters the converter. From this converter the house 

 services are taken. If a supply of both heat and power is 

 required, double or compound converters are used with two 

 reducing-valves, the power being taken from one and the heat 

 from the other. 



A curve ranger, by Mr. Alex. P. Trotter. The instrument is 

 an application of the twenty-fii-st proposition of the third book 

 of Euclid, viz. the angles in the same segment of a circle are 

 equal. A half-silvered mirror, such as is used in sextants, is 

 mounted on an axis at one end of a bar, the other being pro- 

 vided with a sight. The motion of the mirror on its axis 

 allows its inclination to the sight to be adjusted. To set out a 

 curve, a pole is set up at each extremity, and the mirror is suit- 

 ably adjusted. When the poles are seen, the one direct through 

 the unsilvered part and the other by reflection in the silvered 

 part of the mirror in apparent coincidence, and in the middle of 

 the field as shown by the vertical line engraved on the mirror, 

 the instrument is then at the point on the curve required. The 

 mirror being clamped in position, the observer walks in the 

 direction of the curve, and at suitable intervals places himself 

 so that the poles at the extremities of the curve are seen in 

 apparent coincidence. 



On the application of the transporting power of water to the 

 deepening and improvement of rivers, by Mr. W. H. Wheeler, 

 M.Inst.C.E. The object of the paper is to show that the trans- 

 porting power of water may be applied to the proposed purpose, 

 and that under favourable conditions this can be accomplished 

 by breaking up shoals, or the natural bed of a river, by mechani- 

 cal agency and by mixing the material with the water, and 

 allowmg it to be carried away to the sea or estuary in suspension. 

 The author has designed an improved apparatus, which, whilst 

 disintegrating the shoal, mixes its material with the water, allow- 

 ing it to be effectively transported by the ebb current clear of 

 the channel to be improved. 



THE ANTHROPOLOGICAL PAPERS AT THE 

 BRITISH ASSOCIA TION. 



'X'HE work of the Section commenced on Thursday, September 

 -*■ 12, by Mr. Francis Galton, F.R.S., reading a paper on 

 the advisability of assigning marks for bodily efficiency in the 

 examinations of candidates for the public services. In the 

 recent report of H. M. Civil Service Commissioners, they state 

 that, a scheme of competition for physical qualifications having 

 been brought before the notice of the War Office, it was not 

 accepted, on the ground that the authorities were "^completely 

 satisfied with the physique of the young men who came ta 

 them through our examinations." The marks, as at present, of 

 the candidates whose places lie near the dividing line between, 

 success and failure, run pretty evenly ; therefore it is contended 

 that the State would obtain better servants if such moderate 

 marks were allowed for physical qualifications as to insure the 

 selection of the most efficient in body from among those who- 

 are nearly on a par intellectually. 



Mr. Galton also read a paper on the principle and methods- 

 of assigning marks for bodily efficiency. Two separate con- 

 siderations are involved in the just determination of a scale of 

 marks, which are usually mixed up in unknown proportions. (l) 

 Absolute performance — on the principle that if the daily output 

 of one man is greater than that of another, he should be more 

 highly paid, or marked, in that proportion. (2) Relative rank- 

 on the principle that superiority, however small, insures success 



