February 12, 1920] 



NATURE 



647 



satisfactorily in daylight, should be required, in a 

 trial trip at night, to show himself capable of driving 

 in dim light and under varying degrees of illumination. 

 (2) In an examination by an ophthalmic surgeon he 

 should show : (a) Visual acuity of 6/9 in one eye 

 and 6/24 in the other eye, with glasses if necessary ; 

 (b) a full field of vision in each eye ; and (c) no double 

 vision. 



" ¥or Grade C Certificate. — (i) Every applicant 

 should be required in a trial trip to show himself 

 capable of driving a motor-tramcar by day and by 

 night under varying degrees of illumination. (2) In 

 an examination by an ophthalmic surgeon he should 

 reach the same visual standards as for a Grade A 

 certificate." 



The council has clearly taken great pains to con- 

 sider the subject in all its manifold bearings. The 

 recommendations appear to be adequate and reason- 

 able, and there is evidence that the authorities are 

 favourably disposed to them. 



INERTNESS OF INDUSTRIAL 

 EXPLOSIVES. 



"C*ROM Western Australia we have received an 

 •*■ interesting report on investigations into the 

 development of inertness in industrial explosives of the 

 nitro-compound class by Mr. E. A. Mann, Chief 

 Inspector of Explosives, and his colleague, Mr. T. N. 

 Kirton (Perth, W.A. : Government Printers). These 

 investigations were started in 1912 in consequence of 

 repeated complaints from the mines that the e.xplo- 

 sives supplied failed to do the work expected of them. 

 That these complaints were not without foundation 

 was soon ascertained by obtaining samples of the 

 explosive under suspicion and testing their velocities 

 of detonation. The method employed was the well- 

 known D'.Vutriche system, by which the velocity 

 is calculated in relation to the meeting point of 

 detonations of " cordeau d^tonant " or T.N.T. 

 fuse initiated at either end by detonators em- 

 bedded at a fixed distance from one another in 

 the sample under test. The results were startling, 

 and in some instances almost incredible had thev not 

 been confirmed by excellent photographs. One of the 

 most striking cases is perhaps that of a gelignite cart- 

 ridge both ends of which were shattered by the detona- 

 tors attached to the T.N.T. fuse, while the main 

 body of the cartridge remained intact. This is, of 

 course, an extreme case, but in several instances the 

 velocity of detonation was found to be as low as a 

 few hundred m.p.s. as compared with about 2300 

 m.p.s. on arrival in the country. .Another significant 

 feature is that these inert samples have invariably 

 increased in density from about 160 on arrival to 

 about 1-69. 



.Although a certain d'egree of after-gelatinisation, 

 with consequent reduction of sensitiveness to detona- 

 tion, is a recofjnised phenomenon even in this countrv, 

 it has not been sufficient to have any practical effect 

 in our temperate climate ; but as a result of this 

 report it cannot be denied that, so far as our Oversea 

 Possessions are concerned, the matter is of consider- 

 able importance, and deserves the consideration 

 which we understand our leading manufacturers are 

 giving to it. From concurrent observations which the 

 writers of the report have made in regard to the 

 alteration in the viscosity of the nitro-cotton when 

 extracted with amvl acetate, they are disposed to 

 attribute the phenomenon to a change in the molecular 

 structure of this ingredient, and the further investig.-i- 

 tions they promise will be interesting. 



NO. 2624, VOL. 104] 



FLOW OF ]]'ATER THROUGH A PIPE. 



AP.APER entitled "The Orifice as a Means of 

 Measuring the Flow of Water through a Pipe " 

 describes experiments made by Messrs. Davis and 

 Jordan, of the Engineering Experiment Station of the 

 University of Illinois (Bulletin 109), to determine the 

 practicability of measuring the flow of water in a pipe 

 line by means of the pressure drop across a circular 

 orifice in a thin plate diaphragm inserted at a pipe 

 joint. The experiments, which covered a range of pipe 

 diameters ranging from 4 in. to 12 in., show that as 

 a temporary measuring device, or where the loss of 

 head produced by the diaphragm is not serious, the 

 method is capable of useful application. Measuring 

 the upstream head at a point 08 of the pipe diameter 

 from the diaphragm, and the downstream head at a 

 point 04 pipe .diameter from the diaphragm, the dis- 

 charge is proportional to the square root of the difTer- 

 ence of these heads. For a given pipe, the discharge 

 coefficient varies slightly with the diameter of the 

 orifice and with the velocity of flow. So long as the 

 ratio of the diameters is between 2 and 8, the variation 

 is, however, small. For measurements in which an 

 error of 2 per cent, is not serious, the discharge may 

 be taken as given by : — 



Q = .\K\/h cub. ft. per sec. 



where .\ is the area of the pipe in sq. ft. 



,, h is the difference of head on the two sides of 

 the orifice. 



''^i,-Zi 



mQ)- 



Tables showing the accurate values of K for different 

 diameters of pipe and of orifice are given in the original 

 paper. The device would appear to be of value for 

 field service, as being capable of easy and inexpensive 

 application, since in a flanged pipe system the 

 diaphragm may be inserted at a joint with little or 

 no disturbance of the existing piping. 



APPLICATIONS OF AMPLIFYING 

 ELECTRIC VALVES. 



ML. BLOCH communicates an interesting paper 

 • on the industrial applications of the amplifying 

 valves used in radio communication to the J^eriite ician- 

 tifique of January 10. When the vacuum is almost 

 perfect these valves can be used to increase the ampli- 

 tudes of high-frequency oscillations at least a thousand- 

 fold. Their great advantage is that they act as if devoid 

 of inertia, and so completely solve the problem of a 

 telephonic relay. They are already in use in long- 

 distance telephony. . For alternating currents of low 

 frequency the vacuum in the valves does not need to 

 be nearly so high. If argon is used a vacuum of 

 3 cm. suffices, and currents as large as five amperes 

 can pass through the valve. The valves can be use- 

 fully employed for charging accumulators from 

 alternating-current circuits. .Another important ap- 

 plication is for measuring very small currents and 

 pressures. The currents are magnified a thousand 

 times, and then they actuate direct-reading instru- 

 ments. Bv their use the messages sent from the 

 powerful -American radio stations at Annapolis and 

 New Brunswick can be recorded on a Morse ribbon 

 in Paris, "they were much used in "earth-telegraphy " 

 during the war. Two conductors were fixed in the 

 ground about 50 metres apart, and a source of high- 

 frequency current and a microphone were connected 

 between the conductors. The receiving circuit was 



