466 
THE ASTRONOMER ROYAL ON THE COMPARISON OF 
blishment of galvanic wires which would record, perhaps upon the same photographic 
sheet which bears the declination and horizontal force, the magnitude and direction of 
earth-currents in two directions. I conceive that this may be justly regarded as an im- 
portant physical experiment ; and I hope to be able shortly to lay before the Visitors 
some details of plan, and to ask their opinion in a more precise form.” The Board, 
after consideration of my proposals, resolved “ that it be recommended to the Board of 
Admiralty that two lines of insulated wires be established from the Boyal Observatory 
to the stations near Dartford and Croydon, with suitable apparatus at the Royal Obser- 
vatory for the purpose of registering the intensity and direction of terrestrial galvanic 
currents dependent on natural causes at present obscure.” 
Mr. Walker, in his paper in the Philosophical Transactions, 1861, alluded to the 
matter as having come before him, and as having been the subject of his Report and 
Estimate; and added, “I have, to a certain small extent, made progress in anticipation.” 
On 1861, August 14, I submitted a Memorial to the Lords Commissioners of the 
Admiralty on the advantage of erecting the necessary wires and recording apparatus, at 
an estimated expense of £250; and on August 19 I received Their Lordships’ sanction 
to my placing that sum on the Navy Estimates for the Financial Year 1862-1863. On 
August 24 I made formal application to the Directors of the South-Eastern Railway for 
permission to place the wires on the poles of their Telegraph, and on December 20 I 
received their assent. The terms on which this assent was granted were most liberal ; 
no stipulation being made except for the nominal annual rent of five shillings for the 
use of the poles and five shillings for the maintenance of the wires in a state of repair. 
And I take this opportunity of adding that, when it was found that, by the adoption of 
insulators of a high class, the expense was made to exceed the estimate, Messrs. Silver, 
the contractors for the insulators, at once resigned all profit. The whole of the wire- 
work has been done at cost price. 
The wires were completely established under the superintending care of Mr. Walker 
about the autumn of 1862. The wire is that technically called No. 8, ^ inch in dia- 
meter, annealed iron wire, coated with zinc by galvanic deposit. The insulators consist 
each of a double ebonite cup with outer porcelain cup. From the Observatory to the 
Railway, the wires at different times have been led by different channels, but are now 
led underground. The connexions with earth have been made in various ways, but at 
present they are made at each of the three stations by soldering the wires to water-pipes. 
The plan for forming, on a revolving cylinder (covered with photographic paper), a 
spot of light whose position should depend on the galvanic current passing through the 
wires, was arranged at the beginning of 1863. Each wire communicates with the coil 
of a galvanometer. It may be mentioned here that the current has proved far stronger 
than was anticipated. At first, a nearly astatic combination of needles was provided ; it 
was speedily found necessary to turn the red * ends of the needles in the same direction ; 
* By the red end of a needle, I mean that end which is charged with austral magnetism, and which when 
the needle is freely suspended turns to the north magnetic meridian. 
