112 ME. C. V. WALKEE ON MAGNETIC STOEMS AND EAETH-CUEEENTS. 
Fig. 8 is prepared from observations made on September 7, 1860. My observations on 
that day were close and frequent, and a very large number were recorded. As it was not 
easy to trace the curve complete with a five-minute period between the verticals, I have 
therefore limited them to 2^ minutes ; ■ so that the Greenwich curve is expanded in the 
proportion of 1 : 9. There is a considerable resemblance between the two curves in this 
case also. It was a little ditficult to read off the Greenwich photograms on this magni- 
fied scale ; the inflections I have traced out seem a little in arrear of those of the galva- 
nometer. I am unfortunately almost without night observations, and am thus unable 
to make comparisons with some more manageable and conspicuous portions of the 
photograms. Other portions I have been constrained to pass over when the movements 
of the magnets have been continuous, and the photogram has been so accurate that a 
wide white band with jagged projections was recorded. 
My morning observations on September 7 were many and good. I would fain have 
compared them with the Greenwich photogram ; but it was unfortunately defective for 
those hours ; and, by a strange coincidence, on turning to the Kew tracing, the photo- 
gram there was defective at the same time. 
I could scarcely expect to find a rigid correspondence between the two classes of 
results. The causes of magnetic disturbance are evidently of a mixed character, and 
remain to be determined. But I think the comparisons I have made between the 
movement of the magnet and the direction of the current, which, if not wholly, was, as I 
believe, in large part concerned in causing it to move, are sufficiently encouraging. 
Results of a more definite character would of a surety follow from a system of well-con- 
certed observation, made under more favourable circumstances than we can expect to enjoy. 
My attention was naturally directed also to the behaviour of the horizontal-force 
magnet during the times when the earth is thus active with electric currents. The 
position of the horizontal-force magnetometer is given by W.E. in fig. 5, Plate III.,— the 
magnet being at right angles to the magnetic meridian, or to the declination magnet 
N.S., its marked or north end being to the west, or in the position W. The tendency 
of the horizontal-force magnetometer under the influence of earth-currents is to take the 
position of the dotted line A B, at right angles to the resultant line R R'. The declino- 
meter has a tendency to the same position under similar influence ; so that, if no other 
causes than earth-currents were in operation, the motion of the horizontal-force mag- 
netometer would be towards the north when that of the declination magnet was /ro??! 
the north, and vice versd. And regarding the magnets merely as magnets, and without 
reference to the constrained suspension of the one as compared with the more free 
suspension of the other, the reaction of the earth-currents on the horizontal-force mag- 
net might be expected to be greater than upon the declinometer, because of the less 
angle it makes with the resultant R R'. It might therefore be expected, as far as these 
sources of disturbance are concerned, that an increase of horizontal force would coin- 
cide with an increase in declination. This could hardly be expected to come out in every 
case, on account of the other and recondite causes of disturbance that are ever present. 
