466 KEPOKT— 1881. 



Lave been taken of the magnetic elements, but the curves have been laid 

 aside, and very little use has as yet been made of them. 



At the meeting of the British Association last year at Swansea, I laid 

 before the Mathematical and Physical Section an account' of a com- 

 parison of the Declination Curves taken by precisely similar instruments 

 at six European magnetic observatories, viz., Kew, Stonyhurst, Coimbra, 

 Lisbon, Vienna, and St. Petersburg. Since that time I have had the 

 opportunity, through the kindness of the Kew Committee, of studying 

 the horizontal force curves from these stations, the vertical force 

 curves from some of them as well as the declination and horizontal 

 force curves from Melbourne, and from Zi-ka-Wei in China, for the same 

 period (March 1879). I have also compared the curves from these 

 stations, and from Toronto, for the violent magnetic storm which took 

 place in August, 1880. I have now to bring before you some further 

 points which come out of these comparisons. 



It must be remembered that at stations near the poles the horizontal 

 force is smaller in proportion to the total force than it is at stations near 

 to the equator, so that the same disturbance will produce less effect on 

 the horizontal force or on the declination needle, in latitudes near the 

 equator. 



Also the needles at different stations are by no means in the same 

 state of sensibility, and even at the same station they change with time, 

 so that they are not always equally sensitive, and when they lose their 

 magnetism they have to be re-magnetised. 



Let us take first the disturbances on March 15-16, 1879. (See 

 Plate VIII.) We see that soon after 10 a.m. G.M.T., on March 15, 1879, 

 thei-e is a disturbance wave, showing first a diminution and then an 

 increase in the horizontal force at St. Petersburg, Vienna, Kew, and 

 Lisbon. At Melbourne, in Australia, there is a similar disturbance at 

 the same time, both in the declination and in the horizontal force. 



Again, between 2 and 3 p.m., and between 4 and 5, there are very 

 small disturbances, showing themselves at the same absolute time in the 

 horizontal force and declination curves. About 5.20 p.m. there is a well- 

 marked increase in the horizontal force and eastward deflection of the 

 declination needles. 



About 9.30 p.m. G.M.T., a storm begins, which lasts for about an hour. 

 It is felt in the northern and in the southern hemispheres, near to and 

 on both sides of the equator. At all European stations the horizontal 

 force is increased during the first part of the storm, and then diminished. 



At Lisbon the vertical force is first increased and then diminished, 

 and at St. Petersburg and Stonyhurst there is a diminution in the ver- 

 tical force at the same time as at Lisbon. If we regard the declination 

 needles we find that at St. Petersburg, Zi-ka-Wei and Melbourne, and at 

 Bombay the declination westward is first increased and then diminished, 

 whereas at Kew and Lisbon the motions are in the opposite direction. 



The declination at Vienna seems to be intermediate between Kew and 

 St. Petersburg, but the curve is incomplete. At Bombay and the 

 Mauritius, near to, but on opposite sides of, the equator, the declination 

 needles are deflected opposite ways. The deflections are small, because 

 the needles are not sufficiently sensitive. The local time at these places 

 was from 1 to 2 o'clock at night. 



' See British Association Meport for 1880. 



