79 
Experiments and Discoveries. 
eer found, that, with equal dips, north and south, he had equal 
local attractions, but reversed in direction : and the whole of the 
foregoing table indicates the same change, the north end of 
the needle being drawn forward, while the dip is north, and the 
south when the dip is south, at least the exceptions are only in 
places near the magnetic equator, and the amount of the diffe- 
rence in these cases never exceeds a few minutes of a degree. 
The general decrease of effect from England to the equator, the 
increase again from the equator to Cape Horn, and the decrease 
thence as the southern latitudes diminish, are striking instances 
of the accuracy of the method of correction proposed. To which 
I may also add, as a still stronger case, the variations as found 
with and without the plate, in experiments 31, 32, 33, in 
which the greatest difference 
Without the plate, is • * 2 ° 53' 
With the plate, only * * 0° 14/ 
1 
i 
it is thus rendered obvious, that the plate, as fixed in Ports- 
mouth Harbour, in Lat. 50° 47' N., will correct the local at- 
traction of a vessel in Lat. 60° 56' S. ; the dip in the former 
case being 70° north, and in the latter about the same south. 
In short, it is rendered evident from the experiments made in 
the Conway, that the method of correction proposed is appli- 
cable through all navigable latitudes from 50° north to the high- 
est approachable southern regions. 
Only one point could now be considered as doubtful, respect- 
ing the efficacy of this method of correction. It had been as- 
certained by the observations of Captains Ross and Parry, that 
the effect produced by the iron of the ship increased with im- 
mense rapidity, and amounted to the most fearful quantity in ap- 
proaching towards the pole: Would the plate increase in power 
with equal pace? To ascertain this point, Lieutenant Foster, 
who had already received the thanks of the Board of Longitude 
for the experiments on this and other scientific subjects in the 
Conway , was now appointed to the Griper , which was about to 
leave England for Spitsbergen, under the command of Captain 
I). C. Clavering, with orders to continue his experiments on lo- 
cal attraction under the superintendence of the above officer at 
every opportunity. 
W e are sorry we are not able to give the entire detail of these 
experiments, which are the more interesting as they were made 
