ME. C. V. WALKEE ON MAGNETIC CALMS AND EAETH-CUEEENTS. 
213 
see the result of uninterrupted observations, which cannot be obtained from our highly 
occupied telegraph wires. 
I purpose erecting these wires as soon as the insulators are made ; which will be con- 
structed with great care, of a double concentric cup of ebonite, with an outer cup of 
French porcelain. The ebonite cups will be turned in a lathe before fitting, so as to 
present a perfectly smooth surface. They will be placed on the apex of our telegraph 
poles*. 
Four exceptional cases presented themselves among the 276 observations. Their 
character is given in Table XV. They are beyond the reach of the system of analysis 
we have adopted. Whether the general direction of the current-drift was changing at 
the moment of observation, and was complete in one part of the district and not so in 
the other, I cannot, with these very rare and isolated data, pretend to say. The results 
are given precisely as read off. There was no reason to suspect any interferences from 
artificial currents ; a few more cases may throw more light on this exceptional class. 
A few entries will be found in the Table XIII. as thus: 5'’ to 15°; 0° to 10°; 5° u to 
5° &c. The derived currents in these cases were unstable. A few of the earlier cases 
that occurred were questioned, and I was disposed to reject them, the impression being 
that they were due to interference from strong telegraph currents entering into the 
observing-whe. But instances occurred in which there was no reason to suspect inter- 
ferences, they are therefore placed on record. 
We speak of electric currents in this inquiry ; the word conveys the idea of length • 
without width. The currents in question necessarily and evidently cover large areas, 
presenting as it were an electric plane. Passing on from the determination of mere 
direction, I was able to survey the two sides of the same plane. By reference to the 
map (vol. 159, Plate II.), the EamsgateHarbour-London and the Dover-Tonbridge 
lines are not many degrees from being parallel. They are about 20 miles apart ; the 
former is 67 miles, and the latter 45 miles in length. I have at Ashford junction a turn- 
plate or switch. When desiring to make the observations on the Ramsgate-London 
line, I call Ashford and give the word “ branch ;” the reply is “ yes ” or “ no,” accord- 
ing as it is at liberty or not. If at liberty, the switch is turned, and I have the command 
of the wire from Ramsgate to London, the telegraph length of which is 97|- miles ; and 
then, by placing the plug in the hole 3 of fig. 9, for reasons already explained, the 
command is obtained of the Ramsgate-Tonbridge line. 
Observations of this kind have been made from time to time ; the results are given in 
Table XVI. The letters in this and subsequent Tables have the same references as 
those in Table XIII. 
* I completed the two wires, and handed them over to the Astronomer Eoyal, June 30, 1802. 
