CONCEENED IN PEODECING THE GEEATEE MAGNETIC DISTHEBANCES. 623 
Let X be the value of the north and south, and y that of the east and west component 
of a current as deduced from its effects upon the magnetographs. 
This will give on the Margate and Ramsgate line a current represented by 
A-|^ cos 8° 40'+?/ sin 8° 40'[, (!•) 
while for the Ramsgate and Ashford line we shall have 
BjiT cos 83° 50'+^ sin 83° 50'j-, (2.) 
and for the Margate and Ashford line 
C{?rcos77°42'+?/sin77°42'[, (3.) 
where A, B, C are positive constants depending upon the nature of the soil and strata 
along the various lines. 
Now in the disturbance of 8th to 10th August 1860, the declination and horizontal 
force were increased simultaneously, or they were diminished simultaneously ; hence 
X and y have the same sign, and the expressions within brackets are either all positive 
or all negative, that is to say, the currents between these lines should have been either 
all north or all south simultaneously. This was observed to be the case. In this instance, 
therefore, there is nothing to contradict the hypothesis which makes earth-currents the 
cause of magnetic disturbances. 
Let us now examine the disturbance of August 29 to September 2, 1859. Here the 
horizontal force was increased when the declination was diminished, and vice versd ; and 
if we represent by unity the current influential in disturbing the former element, that 
disturbing the latter is most probably represented by — *46 (see Table V.). 
Hence (1.), (2.), (3.) become 
(1) =A|--46cos 8°40'+sin 8° 40'} =--304 A, 
(2) =B|--46 cos 83° 50'+sin 83° 50'} = + -945 B, 
(3) =C}--46 cos 77° 42'+sin 77° 42'} = + -879 C. 
We thus see that in this disturbance, for the theory to hold good, currents of one 
name should have traversed the line between Margate and Ramsgate, while currents of 
the opposite name traversed the other two lines ; but this is not in accordance with the 
observations made, which showed that currents of the same name traversed the three 
lines simultaneously. In one word, the proof against the theory of the direct action of 
earth-currents in causing disturbances may be summed up by saying that, while the 
magnetic disturbances of September 1859 and August 1860 were of opposite character, 
the corresponding earth-currents, as determined by these three telegraphic lines, were of 
the same character. 
6. At flrst view it would almost appear as if this fact, which seems conclusive against 
earth-currents (at least those earth-currents observed in this country) being the direct 
and main cause of disturbances, were equally conclusive against their being induced 
currents, since the effect of such upon the telegraph needle might be supposed opposite 
in character to that which would be produced by such currents as would directly cause 
magnetic disturbances, the two effects being antithetically and therefore definitely related 
to each other. 
4 Q 
MDCCCLXII. 
