te "" REPORT— 1861. 



witli Dr. Lamont, of Municli, and had received the following communications from 

 him on the subject, which he had thouglit it desirable to have printed for the mem- 

 bers of the Association, hut not necessarily for circulation amongst the public gene- 

 rallv. In one of his communications Dr. Lamont said, " Since the beginning of last 

 year I have been occupied with the investigation of the electric currents observed 

 m telegraph wires, and have obtained various results ; the most remarkable of which 

 is this, that electric cun-ents, or, as they may be more properly tanned, electric 

 waves, varying in direction and intensity, are constantly passing at the surface of 

 the earth, and that these waves con-espond perfectly with the variations of terres- 

 trial magnetism ; a wave directed from north to south producing an increase of 

 westerly declination, and a wave directed from east to west producing an increase 

 of horizontal force. I have employed wires of different lengths, and metallic discs 

 of difierent sizes and at difterent depths imdergTOund : in all cases the currents are 

 the same ; but their intensity depends on the size of the discs and the length of the 

 wires, or rather, the distance at which the discs are placed from each other. A 

 distance of 400 feet is sufficient if the discs are large enough. To show the effects 

 satisfactorily, the instruments must be of a peculiar construction ; ordinary galvano- 

 meters and magnetometers will not answer ; besides, various other conditions are 

 to be observed." And in another communication he stated that "The currents 

 observed in telegraph lines are due partly to the agency of chemical causes (oxida- 

 tion of the discs and other parts of circuits), partly to thermal causes (thermo-elec- 

 tricity, expansion, &c.), partly to terrestrial electricity. The variations of ten-estrial 

 electricity can only be obtained while the chemical and thennal causes remain con- 

 stant. The effect of the chemical causes changes very slowly ; the effect of the 

 thermal causes can be considered as constant only in calm weather, and for very 

 short intervals of time (say two or three minutes) when the wires are of moderate 

 length and suspended in the air, for longer intervals if underground. I believe that 

 lines above 1000 feet in length, if not underground, are of no use for the investiga- 

 tion of terrestrial electricity, because under all atmospheric circumstances the 

 disturbances produced by thermo-electric currents will be too great.'' It appeared 

 to him, with very gTeat submission to Dr. Lamont, that they need not necessarily 

 be bound or restricted to the limits which he suggested. As the disturbances 

 aflected long lines of telegrapliic wires, it appeared to him that their attention ought 

 more particularly to be directed to these long lines. He had brought the matter 

 before the Section with the view of inviting discussion upon it. He should be 

 happy to hear from the Section whether they were prepared to adopt the views of 

 Dr. Lamont or his o'^ii, which, he might say, he had now power from Government 

 to carry out. He should be glad if any gentleman would throw out suggestions upon 

 the subject. He would not bind himself to act upon them, but at the same time 

 they shoidd have his best attention. 



On the Lcnvs of the Principal Inequalities, Solar and Liitiar, of Terrestrial 

 Magnetic Force in the Horizontal Plane, from observations at the Royal Ob- 

 servatory, Greenwich, ecctendincj from 1848 to 1857. By the Asteonomer 

 Royal. 



The author described shorth' the apparatus (being, in fact, that which was 

 introduced by Mr. Brooke) by which the continued registers of magnetic direction 

 and magnetic force are maintained. For the direction, a fi'eely suspended magnetic 

 bar carries a concave mirror that receives the light radiating from a fixed lamp, 

 and causes it to converge upon a revolving barrel covered \w\t\\ photographic paper j 

 the oscillations of the magnet cause the spot of light to oscillate lengthwise along 

 the barrel ; and as it is easy to compute, from the dimensions of the apparatus, the 

 proportion that exists between a given s^ving of the magnet and the corresponding 

 motion of the spot of light, the oscillations of the magnet at all times of the day 

 may be measured accurately from the photographic record. Tliese oscillations may 

 be conceived as being produced by pertvu'bing magnetic forces in the E. and W. 

 direction, and tlie magnitudes of those perturbing forces may be inferred from the 

 magnitudes of angular oscillation, by remarking tliat an oscillation of 1 ' corresponds 

 to a perturbing furce equal to ^yVir of the whole directive horizontal force. For 

 tlie perturbing magnetic forces in the N. and S. direction, which exhibit themselves 



