C. T. WALKEE ON MAGNETIC STOEMS AND EAETH-CIJEEENTS. 
Ill 
masses of the declination magnetometer, or the horizontal-force magnetometer. 1 
may or may not get changes in direction, when the transitions are quick, that are not 
recorded in the observatories. On the other hand, we on our part may omit to notice 
many changes. The best mode of making the comparison appeared to be to select some 
periods of what appeared the best and most continuous series of earth-current observa- 
tions, and set them nut in curves side by side with the curves registered at Greenwich 
or at Kew. My choice was limited to the series from August 8 to August 12, and that 
of September 7, 1860, which have been before referred to, and given in detail in Tables 
III. to VIII. 
Various photograms of the Greenwich observations are before me, prepared under 
the eye of Mr. Glaishee, and with which I have been' kindly furnished by the Astro- 
nomer Eoyal. General Saeine also promptly supplied me with tracings of the Kew 
photograms, made by Mr. Balfoue Stewaet. 
Plate IV., figs. 6, 7 and 8, shows results of this comparison. I have selected for 
illustration such parts of the photograms and Tables as admitted of ready comparison. 
Fig. 6 comprises the interval between 2.55 p.m. and 6.45 p.m. of August 8, 1860, civil 
time. The ordinary reaction between a magnet in the position of N. S., fig. 5, Plate III., 
and an electric current moving in the diiection of the arrow-headed resultant E E' in 
the same figure, is that the north end of the magnet moves to the right if the current 
is passing beneath it in the du’ection from E to E', to the left if in the reverse direc- 
tion ; that is, a northerly current increases the declination of the magnet ; a southerly 
deo'eases it. The upper curve in fig. 6 shows the value in degrees of the defiections of 
the galvanometer needle taken from Table III. The distance between the horizontal 
lines is 10°; the distance between the vertical lines is five minutes of time. The 
northern currents N. are set otf below the zero line, the southern above, in order to 
correspond with the curves on the photograms. The lines are left broken where 
observations are wanting. 
The lower curve is taken from the Greenwich photogram of the variations of the 
declination magnet, but is expanded so as to correspond in time with the galvanometer 
cmve. It w’as found more practicable to expand the Greenwich than to contract the 
galvanometer curve. It is expanded in the proportion of 1 : 4’5. A portion of the 
dechnation scale, extending from 21° W. to 21° 45' W. is attached. From 3.15 to 3.57 
the photogram was defective. The general correspondence between the two curves is 
apparent. This is particularly the case at 4; 4.30; 4.45 to 5.15; 5.15 to 5.25; 5.30; 
and thence in the general range to the end of the curve. 
Fig. 7 contains the interval between 2 p.m. and 5.50 p.m., August 9, 1860. The curve 
of the dechnation magnet in this case is taken from a tracing of the Kew photogram. 
It is expanded in the proportion of 1 : 4. I had not the scale before me ; the omission, 
however, is of no moment, for we are merely comparing general directions, not values. 
These cuiwes do not correspond so fully as those of fig. 6 ; but in the more active 
portions the resemblance is sufficiently obvious. 
