74 



NATURE 



[]\Iav 



•J>95 



came to deal with submarine cables, in which the same 

 capacity effect is met with. The second point was the 

 obsen-ation that ven- strong earth currents — that is, 

 electric currents through the crust of the earth — were 

 produced whenever the aurora borealis was visible. 



There is one paper which, although it is included in 

 the first volume, certainly describes a rather amusing 

 practical application of electricity. Werner Siemens, 

 with a party of friends, had ascended the Cheops pyramid, 

 and after reaching the top they noticed that the wind, 

 which had been continually increasing in strength, was 

 raising the sand of the desert with a continuous whirling 

 motion. " When it had arrived at the highest step we 

 noticed a whistling noise, which 1 ascribed to the in- 

 creasing violence of the wind. The Arabs, who were 

 squatted around us on the nearest steps, sprang up 

 suddenly with the cry ' Chamsin,' and held up their fore- 

 finger in the air. There was now a peculiar whistling I 

 noise to be heard, similar to that of singing water. We 

 thought at first that the Arabs were uttering this sound, 

 but 1 soon satisfied myself that it also took place when 

 1 stood upon the highest point of the pyramid and held 

 up my own forefinger in the air. There was also a slight, 

 hardly perceptible, prickling observable on the skin of 

 the finger which was opposed to the wind. I could only 

 explain this fact, observed by all of us, as an electrical 

 phenomenon, and such it proved to be. When I held 

 up a full bottle of wine, the top of which was covered 

 with tinfoil, I heard the same singing sound as when 

 the finger was held up. .-Vt the same time little sparks 

 sprang continually from the label to my hand, and when 

 I touched the head of the bottle with my other hand, 

 I received a strong electric shock. It is clear that the 

 liquid inside the bottle, brought into metallic connection 

 with the metallic covering of the head of the bottle 

 through the damp cork, formed the inner coating of a 

 Leyden jar, whilst the label and hand formed the outer 

 coating. When I had completed the outer coating of 

 my bottle by wrapping it in damp paper, the charge 

 was so strong that I could make use of it as a \ery 

 powerful weapon of defence. .After the Arabs had 

 watched our proceedings for a time with wonder, they 

 came to the conclusion that we were engaged in sorcer>', 

 and requested us to leave the pyramid. .\s their remarks, 

 when interpreted to us, were without effect, they wanted 

 to use the power of the strongest to remove us from the 

 top by violence. I withdrew to the highest point, and 

 fully charged my strengthened flask, when the .\rab 

 leader caught hold of my hand and tried to drag mc 

 away from the position 1 had attained ; at this critical 

 moment I approached the top of my flask to within 

 striking distance of the tip of his nose, which might Ijc 

 about lo m.m. The action of the discharge exceeded 

 my utmost expectation. The son of the desert, whose 

 nerves had never before received such a shock, fell on 

 the ground as though struck by lightning, rushed away 

 with a loud howl, and vanished with a great spring from 

 our vicinity, followed by the whole of his comrades. 

 We had now a full opportunity of carrying out our 

 experiments." 



Before i860, when Siemens published his paper 

 on a reproducible unit of resistance, there was no 

 generally accepted unit, so that it was impossible 



NO. 1334, VOL. 52] 



to compare the results obtained by any one observer 

 with those obtained by any other. The need of 

 such a unit is ver\- well illustrated in one of the early 

 papers in these volumes, where the unit of resistance used 

 in an investigation is said to be the resistance of an iron 

 telegraph wire 2 m.m. thick and 100 Russian versts long I 

 At the present day, with our well-defined systems of 

 electrical units, it is almost impossible to imagine the 

 difficulty and confusion which must have existed when re- 

 sistances, to take one example, were stated in such terms 

 as that mentioned above. It is true that Jacobi had 

 previously proposed as unit the resistance of a certain 

 copper wire in his possession, and had issued copies 

 of this unit. These copies, however, \aried so much 

 one from another as to be quite useless for the more 

 refined and accurate measurements which the previously 

 mentioned tests for localising the faults in underground 

 conductors rendered necessary. Weber also had pro- 

 posed his "absolute" unit of resistance, but at this time 

 no trastworthy experiments had been made so as to 

 embody this " absolute " unit in a material resistance. 

 Siemens was thus led to the adoption of another arbitrary 

 unit of resistance, and for this purpose chose the resistance 

 at o' C. of a column of mercurv" 100 cm. long and having 

 a cross section of one square millimetre. He employed 

 mercur>', since it can be comparati\ely easily prepared 

 in a practically pure state, and being a liquid its molecular 

 condition, and hence its resistance, does not alter with time, 

 as it was quite possible that of a solid metallic wire might 

 do. This unit, known as the Siemens unit, came into 

 ver)" general use, particularly on the continent. Never- 

 theless, the Paris Congress in 188 1 decided to use as 

 the international unit of resistance the nearest approach 

 possible to Weber's "absolute" unit, in order to bring 

 the resistance unit into agreement with the other electrical 

 units. On this subject Siemens says : — 



" It was certainly somewhat hard for mc, that my 

 resistance unit, arrived at with so much trouble 

 and labour, which had, speaking generally, made the 

 first comparable electrical measurements possible, then 

 was employed for more than a dcccnnium through- 

 out the world and adopted as the legal inter- 

 national standard resistance for telegraphy should have 

 suddenly to be set aside with my own co-operation." 

 (.Siemens was the German representative at the Paris 

 Congress.) " But the great advantage of a theoretically 

 established system of standards consistently carried out 

 necessitated this sacrifice offered up to science and the 

 public interest." 



One cannot help sympathising with him in this matter, 

 for it is always hard to disown one's own offspring, 

 particularly after they have had a comparative!)- long and 

 brilliant career. 



Most of the earlier papers in both volumes deal either 

 directly or indirectly with telegraphy. In the remaining 

 portions of either volume, however, a ver)' prominent 

 part is played by papers and inventions in connection 

 with the conversion of mechanical energy into elec- 

 trical energy. In connection with a form of magneto- 

 electric machine, /./■. one in which the magnetic field is 

 produced by permanent steel magnets, for use in tele- 

 graphy, Siemens invented a form of armature, which 

 has since been known as the Siemens armature. This 

 armature is shuttle-shaped and has an iron core, the cross 



