334 



NATURE 



[February i, 1900 



acquainted with the needs of the agricuhural classes and the 

 conditions of country life, and that the inspectors should be 

 instructed to see that the curricula of rural schools are differ- 

 entiated from those of urban schools. It was also recommended 

 that in rural elementary schools there should be a continuous 

 course of rural instruction, beginning in the lower standards with 

 object lessons and continued in the upper standards with lessons 

 in natural history and elementary science bearing on agriculture 

 and rural life. With regard to training, it was suggested that 

 provision should be made at certain of the teachers' training 

 colleges for giving practical as well as theoretical instruction in 

 agriculture and horticulture to those students who desired it. 

 With regard to higher agricultural instruction and evening con- 

 tinuation schools it was recommended that the Board of Educa- 

 tion should encourage those county authorities which have not 

 j'et done so to provide or to contribute to school and experi- 

 mental farms and should inspect and report annually on such 

 farms ; that in rural evening schools instruction should be given 

 in such subjects as natural history, botany, and other sciences 

 hearing on agriculture, horticulture, bee and poultry keeping, 

 land measuring, farm accounts, and so on, rather than in such 

 subjects as typewriting, commercial arithmetic, and shorthand. 

 The Duke of Devonshire expressed himself in sympathy with 

 the desire of the Committee to give a more useful and practical 

 character to elementary education in rural districts, and men- 

 tioned certain steps which the Education Department has taken 

 in furtherance of this object. Full consideration was promised 

 to the various suggestions, put forward by the Agricultural 

 Education Committee. The subject is dealt with in an article 

 on p. 332. 



SOCIETIES AND ACADEMIES. 



London. 

 Physical Society, January 26.— Prof. Lodge, F.R.S., 

 President, in the chair. — -A paper by Prof. Ayrton and Mr. 

 Mather, on some developments in the use of Price's guard wire 

 in insulator tests, was read by Prof. Ayrton. For insulation 

 tests made by the direct deflection method the guard wire pro- 

 perly applied affords complete protection against surface leakage 

 when the ends of the cable tested are near the galvanometer, so 

 that it is possible to have the wire connecting the conductor of 

 the cable with the galvanometer terminal "air insulated." A 

 difficulty, however, arises when the ends of the cable are at a 

 considerable distance from the testing instrument ; this may 

 render air insulation impossible. The authors have overcome 

 this difficulty by applying a guard wire along the entire length 

 of the lead. This is done by using a concentric wire to connect 

 the cable and galvanometer, the inner of the concentric being 

 used as the lead and the outer as the guard wire. The principle 

 can also be applied to determine whether a defective piece of 

 cable is bad throughout or bad owing to one or more isolated 

 faults. In this case the cable is placed in two water tanks, one 

 of which is earthed, and the other fairly well insulated. By a 

 suitable arrangement of the guard wire it is then easy to deter- 

 mine the resistance of the wire in the earthed tank, so that by 

 altering the length of this wire the character of the insulation 

 can be determined throughout the whole length of the cable. In 

 referring to some of the earliest experiments with the guard 

 wire made by Mr. Appleyard in 1895, Prof. Ayrton pointed out 

 that the principle had not been applied completely, and 

 that at one point there was a chance of leakage. Mr. Campbell 

 said that the necessity of having a concentric could be obviated 

 by simply hanging the lead from the guard wire by short 

 lengths of material of fair insulation. Mr. Appleyard said 

 that he quite agreed with Prof. Ayrton that the guard wire 

 ought in general to be applied at both ends of all leads, pro- 

 vided that both ends could be got at. The reason it was 

 used at one end only in the experiments on dielectrics 

 made in 1895 was that the far end of the lead was carried into 

 the condenser box, which was submerged in water in the 

 temperature tank. Special precautions were taken to ensure 

 good insulation of the submerged end of the lead, and tests 

 showed that the leakage there was nil. As the end of the wire 

 could not be got at, no guard wire could be applied. Mr. 

 Appleyard congratulated the authors upon the use of a con- 

 cept ric cable for a lead, and pointed out that such a lead was 

 sufficient for all the routine tests on core ; the inner and outer 

 conductors could be used for the purpose of taking the "copper " 

 resistance. Mr. Price expressed his interest in the develop- 



NO. 1579, VOL. 61] 



ments of his principle which had been made by the authors. — 

 Mr. Appleyard then read a paper on a fault-test for braided and 

 other cable-core. This method enables the fault to be found 

 without the removal of braiding or tape. The core is wound 

 on two insulated drums or tanks, the intermediate piece of cable 

 being about ten feet long. One end of the core is left free, the 

 other is connected to earth through a galvanometer and a 

 battery. A guard wire is connected from some point between 

 the galvanometer and the battery to some point of the braiding 

 on the wire between the drums. A wet cloth, connected to an 

 earth wire, is laid on one or other of the drums, over the 

 braiding. The galvanometer deflection is noted. The earth- 

 wire is then changed over to the second drum, and the corre- 

 sponding deflection is observed. A comparison of these 

 deflections at once indicates upon which drum the fault lies. 

 With the galvanometer still deflected, the core may be run 

 through a suitable contact brush or sponge attached to the guard 

 wire. The instant the fault passes under the guard wire contact, 

 the deflection falls and the fault is located. The paper gives 

 the theory of the method, and indicates how to apply it (i) to 

 localising "distributed " faults ; (2) to several faults in a single 

 cable ; and (3) to the case of a single fault. One advantage of 

 the method is that at the critical moment, when the fault 

 passes under the guard wire, the galvanometer is short 

 circuited through the fault, and thus completely protected. — 

 A paper on reflection and transmission of electric waves along 

 wires, by Dr. E. Barton and Mr. L. Lownds, was read by Dr. 

 Barton. The waves used were produced by means of an in- 

 duction coil and an oscillator, and travelled along wires '15 cm. 

 diameter, 8 cms. apart, and 166 metres long. The ends of the 

 wires were connected by graphite markings on ground glass, so 

 that any wave trains which reached the ends were at once 

 absorbed. Three circular parallel-plate condensers were used, 

 of 15, 9 and 5 cms. radius respectively. The plates were in all 

 cases separated by ait, and were placed i cm. apart. The 

 needle of the electrometer connecting the wires was uncharged, 

 so that it was always attracted by the charged plates. The 

 positions of the condenser and electrometer could be varied so 

 as to study either the reflected or the transmitted waves. The 

 electrometer produced a negligible disturbance, as it reflected 

 only o '04 per cent, of the energy incident upon it. The authors 

 have attacked the problem mathematically, using the relations 

 of Heaviside, and have obtained expressions for the reflected 

 and transmitted systems. These expressions consist of two 

 terms, one of which is comparatively unimportant. From the 

 other term certain values have been calculated. A superior 

 limit has then been given to the other term, and the values 

 already obtained have been subjected to a correction on this 

 account. By a suitable arrangement of the condenser and 

 electrometer these calculated values have been experimentally 

 determined, and are in close agreement with the theoretical 

 numbers, falling in many cases between the results derived 

 from the approximate and the corrected theories. The authors 

 have also investigated the stationary wave system produced 

 by interference when the electrometer is placed close to the 

 condenser, and between the condenser and the oscillator. The 

 chairman said that the experiments afforded a satisfactory 

 verification of Heaviside's theory.— A paper on the frequency 

 of transverse vibrations of a stretched india-rubber cord, by 

 Mr. T. J. Baker, was taken as read. In this paper Mr. Baker 

 has investigated the frequency of the note given out by an 

 india-rubber cord of square section when subjected to different 

 tensions. The relation between length and tension is linear 

 over a considerable range. The curve connecting length with 

 frequency shows that while the cord was doubling its length 

 the pitch was rising rapidly, but that further extension was 

 practically without effect. Since the relation between length 

 and tension is linear, while the sectional area is decreasing, it 

 follows that the value of Young's modulus must be changing. 

 The author has shown that the value of Young's modulus is 

 proportional to the square of the stretched length of the cord. 

 Using this fact, the frequency of the note given out by a stretched 

 india-rubber cord is shown to be proportional to a quantity 

 which varies very slightly with increase in length of the cord, 

 and hence the variation in elasticity is given as the cause of the 

 constancy of the note. — Mr. Appleyard exhibited some mirrors 

 produced inside incandescent lamps by the application of 

 voltages much above those for which the lamps were designed, 

 and the consequent deflagration of the filaments. —The meeting 

 then adjourned until February 9. 



