400 



NATURE 



[August 23, 1900 



released easily. The current was from o-oo20 

 to 00027 ampere. 



30 volts. The fingers, hands, wrists, the forearms and upper 

 arms nearly paralysed ; the fingers or hand 

 could scarcely be moved ; serious pains in the 

 fingers, hands and arms, and the experiment 

 not endurable for more than lO seconds. The 

 wires could, however, be released, but only by 

 using the greatest determination. Current, 

 0"0I5 ampere. 



40 volts. The fingers, hands and arms were instantaneously 

 paralysed, and the pain was almost unbearable. 

 The wires could hardly in any case be released. 

 The pain could not be endured longer than 5 

 seconds. 



50 volts. Again instantaneous paralysis of all the muscles of 

 the fingers, hands and arms ; the wires could 

 not be released ; the state endurable for 2 

 seconds at most, whence it was impossible to 

 measure the current. 



Having obtained the above results, the experimenter did not 

 find it advisable to let the pressure exceed the 50 volts ; the 

 fact that when the hands were wet, it was impossible on 50 

 volts pressure to release the wires, seemed to prove to him that 

 serious danger was just beginning at this point. 



With dry hands he formed the following results : — 



P.D.. Effect. 



40 volts. The fingers only tingle slightly ; the current too 

 feeble for measurement. 

 The effects gradually increasing and extending to 

 the arms up to the shoulders, until at 

 80 volts. The fingers, hands and arms were almost cramped 

 and aching in every part ; great effort was 

 required to release the wires ; current from 

 0009 to o'oii ampere. 

 90 volts. At the same moment in which the wire is seized, 

 the hands are absolutely paralysed and the wire 

 cannot be released again. The pains in the 

 hands and arms were so violent that they caused 

 the experimenter to call out involuntarily ; the 

 effects could not be endured for more than 1-2 

 seconds. 



The experimenter now went back to 80 volts, 

 and the difference was so great that the effects 

 of this pressure seemed to be extremely feeble 

 relatively to the effects at 90 volts pressure ; 

 this fact prevented him from trying the effects of 

 pressure higher still 

 From these experiments Prof. Weber draws the following 

 conclusions : — 



" A simultaneous touching of both of the poles of an alter- 

 nating current circuit is dangerous as soon as the pressure 

 exceeds 100 volts ; and since it is impossible to set one's self free, 

 the case must be regarded as fatal whenever immediate help is 

 not at hand." 



These results are consistent with several disasters which have 

 happened in practical life. 



In 1896, in Horgen (Switzerland), a man, to prevent his falling 

 down from a ladder, seized with both his hands two non- 

 insulated leads with a P.D. of 240 volts between them, and was 

 immediately killed. 



In a mine in Silesia a workman seized in the same manner 

 some non-insulated leads and was killed on account of his being 

 unable to release them, the P.D. being 300 volts. 



In the Electric Central Station in Olten a workman, desirous 

 of proving to his companions that a pressure of 500 volts was 

 quite safe, seized both of the leads and was killed instantly. 



From this it is obvious that the general opinion of a pressure 

 of 500 volts not being dangerous does not hold good, the limit 

 being much lower. In spite of the great number of disasters 

 which have already happened, the danger does not seem to have 

 been generally appreciated, and workmen and erectors are often 

 seen to deal with leads and apparatus of relatively high pressures 

 in the most careless manner. That disasters have not taken 

 place far more often may be due to the fact that in most cases 

 help has been at hand instantly. 



Entirely differing from these are the results of the other series 

 of experiments (<5). In this case the person is supposed to 

 fitand at one of the poles itself, namely, the earth, from which 



NO. 1608, VOL. 62] 



he is, however, rather well in.'ulated by means of his shoes; 

 and, as it will be evident from the results, the danger is in thi» 

 case very small even at high pressures. 



The arrangement used for this series of experiments consisted 

 of twenty glow-lamp.s,each for 100 volts pressure, connected in 

 series and all well insulated, the total alternating pressure 

 between the first and the last lamp being 2000 volts. The free 

 terminal of the first lamp was earthed, and between every two 

 consecutive lamps a 6 mm. copper wire was soldered to the 

 main connecting the lamps. Between the earth and the first, 

 second, third to the twentieth of the 6 mm. wires, the pressure 

 was consequently 100, 200, 300, . . . 2000 volts. 



Standing on the ground. Prof. Weber touched the different 

 wires— firstly, merely by a slight touch ; secondly, by firmly 

 gripping them in his hand. The experiments were made under 

 two conditions, the experimenter standing firstly on moist gravel 

 soil, and afterwards on clay covered by a thin layer of coal- 

 dust. 



Standing on moist gravel soil, he obtained the following 

 results : — 



P. D. Eflfect when the wire was 



Slightly touched. Firmly gripped. 



800 volts. Feeble stinging of the No effect, 



skin. 

 Gradually increasing until at 

 2000 volts. Violent stinging of the Intense trembling of the 

 skin. fingers. 



Standing on clay covered with coal-dust, he obtained the 

 following results : — 



P. D. Effect when the wire was 



Slightly touched. Firmly gripped. 



200 volts. Scarcely sensible sting- No effect whatever, 

 ing of the skin. 



fThe fingers begin to tingle 

 feebly. 

 ' !- uraduaiiy mcreasmg. ^ Intense trembling of the 

 ' I fingers, hands, arms and 



^ ankle-joints. 

 1000 „ Stinging like burning The effects in the fingers, 

 by a flame. hands, arms and feet not 



endurable longer than 

 I to 2 seconds ; difficulty 

 in releasing the wire. 

 1300 ,, Same effect. ' The fingers, hands, and 



the arms are entirely 

 paralysed, and the wire 

 cannot be released. 

 From the last series of experiments it will be obvious that 

 to touch one of the poles is not dangerous as long as the 

 pressure does not exceed about 1000 volts ; the intense stinging 

 which appears at the first slight touching serves as a protection 

 against the danger, for the hand is instinctively drawn back 

 rapidly. 



The main result of these experiments is, then, that all pres- 

 sures between 100 and 1000 volts must be regarded as equally 

 dangerous, and consequently there is no reason for not using the 

 higher pressures between 500 and 1000 volts, especially as they 

 lead to greater economy in the working of the electric railway. 

 Further, there is only a very little chance of the passengers or 

 other persons coming into contact with both of the leads. To 

 this danger the employes only are exposed, and being generally 

 people with some electric training, they are acquainted with the 

 danger and may be supposed to be sufficiently careful. 



Finally, it is to be remarked that the authorities after these 

 investigations allowed the use of a working pressure of 75*^ 

 volts as originally proposed. 



500 

 700 



SEA COAST DESTRUCTION AND LITTORAL 



DRIFT. 

 "T^HE increasing number of seaside resorts that are coii- 

 ■*■ stantly being established all round the coast of this 

 country, and the necessity of protecting the sea front from the 

 devastation of the waves, has led recently to greater interest 

 being shown in the protection of the shores and cliffs. 



The means taken to preserve our coasts are as diverse as 

 many of them are ineffectual ; and in many cases are designed 

 without any proper consideration being given to the way in 

 which the waves act, or to the physical conditions which have to 

 be dealt with in the management of the littoral drift ; while 



