27© 



NATURE 



{Feb. 5, 1874 



annual variations and diurnal variations. Every day the needle 

 varies from a few minutes on one side to a few minutes on the 

 other side of its mean position, and at times there are much 

 greater variations. What are called "magnetic storms" are of 

 not very un'requent occurrence. In a magnetic storm the needle 

 will often fly twenty minutes, thirty minutes, a degree, or even 

 as much as two or three degrees sometimes, from its proper 

 position — if I may use that term — its proper position for the 

 time ; that is, the position which it might be expected to have 

 at the time according to the statistics of previous observations. 

 I speak of the needle in general. Tlie ordinary observation of 

 the horizontal needle shows these phenomena. So does obser- 

 vation on the dip of the needle. So does observation on the 

 total intensity of the terrestrial magnetic force. 



The three elements, deflection, dip, and total intensity, all 

 vary every day with the ordinary diurnal variation, and irregu- 

 larly with the magnetic storm. The magnetic storm is always 

 associated with a visible phenomenon, which we call, habitually, 

 electrical ; — aurora borealis, and, no doubt, also aurora of 

 the southern polar regions. We have the strongest possible 

 reasons for believing that aurora consists of electric currents, 

 like the electric phenomena presented by currents of elec- 

 tricity through what are called vacuum tubes, through the space 

 occupied by vacuums of different qualities in the well-known 

 vacuum tubes. Of course, the very expression, "vacuums of 

 different qualities " is a contradiction in terms. It implies that 

 there are small quantities of matter of different kinds left in those 

 nearest approaches to a perfect vacuum which we can make. 



Well now, it is known to you all that aurora borealis is pro- 

 perly comparable with the phenomena presented by vacuum 

 tubes. The appearance of the light, the variations which it 

 presents, and the magnetic accompaniments, are all confirmatory 

 of this view, so that we may accept it as one of the truths of 

 science. Well now— and here is a point upon which, I tliink, the 

 practical telegraphist not only can, but will, before long give to 

 abstract science data forjudging — is the deflection of the needle 

 a direct effect of the auroral current, or are the auroral current 

 and the deflection of the needle common results of another 

 cause ? 



With reference to this point, I must speak of underground 

 currents. There again I have named a household word to every- 

 one who has anything to do with the operation of working the 

 electric telegraph, and not a very pie ising household word I 

 must say. I am sure most practical telegraphers would rather 

 never hear of earth currents again. Still we have got earth cur- 

 rents ; let us make the best of them. They are always with us ; 

 let us see whether we cannot m ike something of them, since they 

 have given us so much trouble. Now, if we could have simul- 

 taneous observations of the underground currents, of the three 

 ma.netic elements, and of the aurora, we should have a mass of 

 evidence from which, I believe, without fail, we ought to be 

 able to conclude an answer more or less definite to the ques- 

 tion I have put. Are we to look in the regions external to 

 our atmosphere for the cause of the underground currents, or 

 are we to look under the earth for some unknown cause affecting 

 terrestrial magnetism, and giving rise to an induction of those 

 currents ? The direction of the effects, if we can only observe 

 those directions, will help us most materially to judge as to what 

 answer should be given. 



It is my desire to make a suggestion which may reach mem- 

 bers of this society, and associates in distant parts of the world. 

 1 make it not merely to occupy a little time in an inaugural ad- 

 dress, but with the most earnest desire and expectation that 

 something may be done in the direction of my suggestion. I do 

 not venture to say that something may come from my suggestion, 

 because, perhaps, without any suggestion from me, the acute and 

 intelligent operators whom our great submarine telegraph com- 

 panies have spread far and wide over the earth, are fully alive to 

 the importance of such observations as I am now speaking o_f. 

 I would just briefly say that this kind of observation is what 

 would be of value for the scientific problem — to observe the in- 

 dication of an electrometer at each end of a telegraph line at any 

 time, whether during a magnetic storm or not, and at any time 

 of the mght or day. If the line be worked with a condenser at 

 each end, this observation can be made without in the slightest 

 degree influencing, and therefore without in the slightest degree 

 disturbing, the practical work throughout the line. Put on an 

 electrometer in direct connection with the line, connect the out- 

 side of the electrometer with a proper earth connection, and it 

 may be observed quite irrespectively of the signalling ; when the 



signalling is done, as it very frequently is at submarine lines, 

 with a condenser at each end. The scientific observation will 

 be di-turbe i undoubtedly, and considerably disturbed by the 

 sending of messages, but the disturbance is only transient, and 

 in the very pause at the end of a word there will be a sufficiently 

 near approach to steadiness in the potential at the eml of a wire 

 connected with the electrometer to allow a careful observer to 

 estimate with practical accuracy the indication that he would have 

 were there no working of the line going on at the lime. A mag- 

 netic storm of considerable intensity does not stop the working, 

 does indeed scarcely interfere with the working, of a submarine 

 line in many instances when a con lenser is used at each end. 



Thus, observations, even when the line is working, may be 

 made during magnetic storms, and again, during hours when the 

 line is not working, if there are any, and even the very busiest 

 lines have occasional hours of rest. Perhaps, then, however, 

 the operators have no time or zeal left, or, rather, I am 

 sure they have always zeal, but I am not sure that there 

 is always time left, and it may be impossible for them to 

 bear the strain longer than their office hours require them. But 

 when there is an operator, or a superintendent, or a mechanic, 

 or an extra operator who may have a little time on his hands, 

 then, I say, any single observation or any series of .observations 

 that he can make on the electric potentials at one end of an in- 

 sulated line will give valuable re-ults. When arrangements can 

 be made for simultaneous observations of the potentials by an 

 electrometer at the two ends of the line, the results will be still 

 more valuibl;. 



And, lastly, I may just say that when an electrometer is not 

 available, a galvanometer of very large resistance may be em- 

 ployed. This will not in the slightest decree interfere with the 

 practical working any more than would an electrometer, nor 

 will it be more difficult to get results of the scientific observations 

 not overpaweringly disturbed by the practical working if a galva- 

 nometer is used than when an electrometer is available. The 

 more resistance that can be put in between the cable and 

 the earth in circuit with the galvanometer the better, and the sen- 

 sibility of the galvanometer will still be found perhaps more than 

 necessary. Then, instead of reducing it by a shunt, let steel 

 magnets, giving a more poweriul direction to the needle, be 

 applied (or adjusting it. The resistance in circuit with the 

 galvanometer between cable-end and earth ought to be at least 

 twenty-times the cable's copper-resistance to make the galva- 

 nometer observations as valuable as those to be had by electro- 

 meter. 



I should speak also of the subject of atmospheric electricity. 

 The electric telegraph brings this phenomenon into connection 

 with terrestrial magnetism with earth current-, and through them 

 with aurora borealis, in a manner for which observations made 

 befure the time of the electric telegraph, or without the aid of 

 the electric telegraph, had not given us any data whatever. 

 Scientific observa'ions on terrestriil magnetism, and on the 

 aurora, and on atmospheric electricity, had shown a connection 

 between the aurora and terrestrial magnetism in the shape of the 

 disturbances that I have alluded to at the time of magnetic 

 storms ; but no connection between magnetic storms and 

 atmospheric electricity, thunderstorms, or generally the state of 

 the weather — what is commonly called meteorology — has yet 

 been discovered. 



The one common link connecting these phenomena hitherto 

 known to us is exhibited in the electric telegraph. A telegraphic 

 line — an air line more particularly, but a submarine line also — 

 shows us unusually great disturbances, not only when there are 

 auroras and variations of terrestrial m.agnetism, but when the 

 atmospheric electricity is in a disturbed state. That it 

 shuuld be so electricians here present will readily understand. 

 They will understand when they consider the change of electri- 

 ficaion of the earth's surface which a lightning discharge neces- 

 sarily produces. 



I fear I might occupy^too much of your time, or else I would 

 just like to say a word upon atmospheric electricity, and to call 

 your attention to the quantitative relations which questions in 

 connection with this subject bear to those of ordinary earth cur- 

 rents and the phenomena of terrestrial magnetism. In fair 

 weather, the surface of the earth is always, in these countries at 

 all events, found negatively electrified. Now the limitation to 

 these countries that I have made sugi;ests a point for the prac- 

 tical telegraphists all over the world. Let us know whether it 

 is only in England, France, and Italy that in fine weather the 

 earth's surface is negatively electrified. 



