110 ME. C. V. W.1LKEE ON MAGNETIC STOEMS AND EAETH-CIJEEENTS. 
original notes made with the published magnetic observations of the Eoyal Observatory, 
1 should scarcely think it possible when we collected electric currents of value so high 
in August and September 1859, by our probes or sounds thrust slightly into the earth, 
that the conducting metallic veins, large in bulk though more deeply beneath the sur- 
face, took no part in the general work of conduction. 
It will be seen that when the direction of the current changes in one length of tele- 
graph wire, it changes also in all the others then under observation ; so that, should 
observations upon earth-currents at any future time form part of the work of magnetic 
observatories, it will by no means be essential to have an absolute N.E. line of wire for 
determining general direction and changes. It may in many cases be inconvenient or 
impracticable to select this direction, — as with the Eoyal Observatory, at this moment. 
In order to obtain maximum results such direction will of course be preferable. Th& 
derived currents collected from the earth are higher in value in proportion as the con- 
ducting wire is larger. It will therefore be better for comparative observations of values 
to select some wire most commonly met with, — as, for instance. No. 8 galvanized iron for 
suspension, being a wire inch in diameter, or, for buried wire. No. 16 copper, a whe 
■j-g inch in diameter. 
On the Map, Plate II., I have laid do^vn the line of direction through Greenwich of 
a Avire coinciding in azimuth with the resultant direction determined herein for the 
earth-currents, I apprehend that a wire extended in this direction from the Eoyal 
Observatory to the Eiver Thames, a distance of a mile or thereabouts, with a sensithe 
galvanometer, or possibly a Webee’s dynamometer in circuit at the observatory, would 
enable the Astronomer Eoyal to study the general direction of earth-currents in juxta- 
position with the movements of the magnetometers, and to obtain photographic registry 
of them side by side with those already recorded of the magnetic variations. For a 
further extension of the system to observations upon the actual azimuth, and the- 
periodical or secular changes in such azimuth, a second Avire in a direction at right 
angles to the other would be essential. Longer wires would necessarily be better. 
It is not my purpose to enter into the complex problem of the magnetism proper of 
the earth, and of its variations. I am not competent to deal with these questions. Happily 
for science, they are well cared for in the hands of our Treasurer, the highly talented 
General Sabine. But having thus far succeeded in determining that there are actual 
cui’rents of electricity, large in amount, travelling in noAV knoAvn directions through the 
mass of the earth, I have been naturally led to look at the magnetometers at observa- 
tories simply as magnets, and to inquire whether their behaviour, during the prevalence 
of these active states of the earth, was in accordance or not with the knoAvn reactions 
of current electricity and magnetism. My inquiries at present are rather tentative than 
complete. My means of observation are less perfect than is the systematic organization 
of an obseiwatory, especially Avhen further aided as it is by the introduction of photo- 
graphy. It may be also that the very small masses of metal of Avhich my needles are 
formed are more readily moved, that is more promptly moved than are the larger 
