od 
ADDRESS. lix 
are periodical changes of the magnetic elements depending on the hour of 
the day, the season of the year, and on what seemed strange intervals of 
about eleven years. Also, that besides these regular changes there were 
others of a more abrupt and seemingly irregular character—Humboldt’s 
‘magnetic storms’—which occur simultaneously at distant parts of the 
earth’s surface. Major-General Sabine, than whom no individual has done 
more in this field of research since Halley first attempted “ to explain the 
change in the variation of the magnetic needle,” has proved that the magnetic 
storms observe diurnal, annual, and decennial periods. But with 
what phase or phenomenon of earthly or heavenly bodies, it may be asked, 
has the maguetic period of ten years to do? The coincidence which 
points to, if it does not give, the answer, is one of the most remarkable, un- 
expected, and encouraging to patient observers. 
For thirty years a German astronomer, Schwabe, had set himself the task 
of daily observing and recording the appearance of the sun’s disk ; in which 
time he found that the spots passed through periodic phases of inerease and 
decrease, the length of the period being about ten years. A comparison 
of the independent evidence of the astronomer and magnetic observer has 
shown that the decennial magnetic period coincides both in its duration 
and in its epochs of maximum and minimum with the same period observed 
in the solar spots. 
A few weeks ago, during a visit of inspection to our establishment at Kew, 
I observed the successful operation of the photoheliographic apparatus in 
depicting the solar spots as they then appeared. The continued regular 
record of the macular state of the sun’s surface, with the concurrent magnetic 
observations now established over many distant points of the earth’s surface, 
will ere long establish the full significance and value of the remarkable, and, 
in reference to the observers, undesigned, coincidence above mentioned. 
Not to trespass on your patience by tracing the progress of magnetism 
from Gilbert to Oersted, I cannot but advert to the time, 1807, when the 
latter tried to discover whether electricity in its most latent state had any 
effect on the magnet, and to his great result, in 1820, that the conducting- 
wire of a voltaic circuit acts upon a magnetic needle, so that the latter tends 
to place itself at right angles to the wire. 
The ablest physicists in Europe, and Ampére especially, devoted them- 
selves, immediately on the promulgation of this capital discovery, to the 
analysis of its conditions. Ampére, moreover, succeeded, by means of a 
delicate apparatus, in demonstrating that the voltaic wire was affected by the 
action of the earth itself as a magnet. In short, the generalization was esta- 
blished, that magnetism and electricity are but different effects of one common 
cause. This has proved the first step to still grander abstractions—to that 
which conceives the reduction of all the species of imponderable fluids of 
the chemistry of our student days, together with gravitation, chemicity*, 
‘ * ‘ Blective’ or ‘ molecular attraction.’ 
