458 EEPOET— 1880. 



certain point of time, the disturbances at all the stations are precisely alike, but 

 suddenly at one or two stations the disturbance changes its character : for instance, 

 on comparing Kew and St. Petersburg, we get perfect similarity followed by de- 

 flections of the needle opposite ways at the same instant, and in some such cases 

 the maxima in opposite directions are reached at the same instant, showing that the 

 opposite deflections are produced by the same cause, and that the immediate cause 

 or medium of distiu-bance in such a case is not far olF; probably it is some change 

 of direction or intensity of the earth's magnetism arising from solar action upon it. 



Generally, after an hour or two, these differences in the effects of the disturbance 

 vanish, and the disturbances again become alike and simultaneous. In such cases 

 of difference, if the curve-tracing of the horizontal or the vertical force be examined, 

 it is generally found that, at the instant when these opposite movements begin there 

 is an increase or a diminution in the horizontal force, and that the horizontal force 

 continues to change as long as there is any difference in the character of the 

 declination curves. It is clear, then, from these effects that the cause or causes 

 of magnetic disturbances are in general far distant from the earth's surface, even 

 ■when those disturbances are large ; but that not unfrequently these causes act on 

 magnetic matter nearer to the surface of the earth, and therefore at times between 

 two places of observation, and nearer to one than another, thus producing opposite 

 effects on the declination needle at those places ; in such cases, the differences 

 are probably due to changes in the earth's magnetic force. Now, if we imagine 

 the masses of iron, nickel, and magnesium in the sun to retain even a slight degree 

 of magnetic power in their gaseous state — and we Iniow from the researches 

 of Faraday that gases, are some of them magnetic— we have a sufficient cause 

 for all our terrestrial magnetic changes, for we know that these masses of metal 

 are ever boiling up frour the lower and hotter levels of the sun's atmosphere to the 

 cooler upper regions, where tbey must again form clouds to throw out their light 

 and heat, and to absorb the light and lieat coming from the hotter lower regions ; 

 then they become condensed and are drawn again back towards the body of the 

 sun, so forming those remarkable dark spaces or sun-spots by their downrush to- 

 wards the lower levels. 



In these vast changes, which we know from the science of energy must be 

 taking place, but of the vastness of which we can have no conception, we have 

 .abundant cause for those magnetic changes which we observe at the same instant 

 at distant points on the surface of the earth, and the same cause acting by induc- 

 tion on the magnetic matter within and on the earth may well produce changes in 

 the magnitude or in the direction of its total magnetic force. These magnetic 

 changes on the earth will influence the declination needles at different places, and 

 will cause them to be deflected ; the direction of the deflection must depend on 

 the situation of the earth's magnetic axis or the direction of its motion with regard 

 to the stations where the observations are made. Thus both directly and indi- 

 rectly we may find in the Sun not only the cause of diurnal magnetic variations, 

 but also the cause of these remarkable magnetic changes and disturbances over 

 the surface of the Earth. 



The following Reports and Papers were read : — 



1. Bejport of the Committee for the Measurement of the Lunar Distvrhance 

 of Gravity. — See Reports, p. 25. 



Report of the Committee upon the present state of our Knoivledge of Spec- 

 trum Analysis. (Influence of Temperature and Pressure on the Spectra 

 of Gases.) — See Reports, p. 258. 



