ADDRESS. ly 
unremitting labour. From a cosmical connexion of this nature, supposing it 
to be finally established, it would follow, that the decennial period which 
we measure by our magnetic instruments is, in fact, a solar period, mani- 
fested to us also by the alternately increasing and decreasing frequency and 
magnitude of obscurations on the surface of the solar disc. May we not 
haye in these phenomena the indication of a cycle or period of secular 
change in the magnetism of the sun, affecting visibly his gaseous atmosphere 
or photosphere, and sensibly modifying the magnetic influence which he 
excicises on the surface of our earth? 
The determination of the figure and dimensions of the globe which we 
- inhabit may justly be regarded as possessing a very high degree of scientific 
interest and value, and the measurements necessary for a correct knowledge 
thereof, have long been looked upon as proper subjects for public underta- 
kings and as highly honourable to the nations which have taken part in them. 
Inquiries in which I was formerly engaged led me fully to concur with a 
remark of Laplace, to the effect that it is extremely probable that the first 
attempts were made at a period much anterior to those of which history has 
preserved the record; the relation which many measures of the most remote 
antiquity have to each other and to the terrestrial circumference strengthens 
this conjecture, and seems to indicate, not only that the earth’s cireumference 
was known with a great degree of accuracy at an extremely ancient period, but — 
that it has served as the base of a complete system of measures the vestiges of 
which have been found in Egypt and Asia, In modern times the merit of re- 
suming these investigations belongs to the French nation, by whom the are of 
the meridian between Formentera and Dunkirk was measured towards the close 
of thelast century. The Trigonometrical Survey of Great Britain, commenced 
in 1783, for the specific object of connecting the Observatories of Greenwich 
and Paris, was speedily expanded by the able men to whom its direction was 
then confided into an undertaking of far greater scientific as well as topo- 
graphical importance, having for its objects on the one hand the formation 
of correct maps of Great Britain, and on the other the measurement of an 
are of the meridian, having the extreme northern and southern points of the 
Island for its terminations. A portion of this are, amounting to 2° 50’, viz. 
_ from Dunnose in the Isle of Wight to Clifton in Yorkshire, was published in 
_ the Phil. Trans. in 1803. As the whole arc, extending from Dunnose to 
 Unst and Balta, the most northern of the Shetland Islands, would comprise 
- more than 10°, and as nearly half a century had elapsed since the publication 
| the solar spots which M. Schwabe has established by twenty-six years of 











use, and by those who were interested for the scientific character of the nation, 
that the general results of the Survey applicable to scientific purposes should 
at length be given to the world. Accordingly, at the Birmingham Meeting 
