220 Proceedings of Philosophical Societies. [Manren, 
and afterwards attempted to point out some of the dangers to 
which navigators are exposed from inattention to the cir- 
cumstances producing such local variations. 
At this meeting also a paper was read, by W. Scoresby, Jun. 
Esq. on the anonialy in the variation of the magnetic needle as 
observed on shipboard. The author began with remarking 
that the anomalous variation occasioned by the iron of the ship, 
first pointed out by Capt. Flinders, is now generally admitted. 
He then proceeded to state his observations upon the subject 
made during the years 1815 and 1817 upon the coast of Spitz- 
bergen, select tables of which observations were given. To 
these were added some general inferences upon the subject, 
deduced at the time of observation, in which it was remarked, 
that the anomaly is probably greater in large ships of war and 
merchantmen carrying much iron than in others, though he 
stated it to be perceptible in all ships, even when iron forms no 
part of the cargo, especially in high latitudes. 
_ There was likewise read at this meeting an extract of a letter 
from T. Say, Esq. of Philadelphia, to Dr. Leach, on the subject 
of the genus Ocythoe. The author commenced by describing a 
new species of ocythoe. This animal is found occupying the 
argonauta shell, residing in its last volute. The shell also does 
not fit the animal, nor is it attached to its body. The author 
supposed it therefore to be a parasite, and that the animal which 
forms the argonauta shell may possibly belong to the order 
pteropoda, though all hitherto observed of this order swim on 
the surface of the water; for having nothing but fins, they are 
not calculated to move along the bottom. 
» There was also read a communication, by L. F. Bastard, of 
Geneva, entitled “ Arithmetical Observations upon the Extrac- 
tion of Roots.” The author offered some remarks upon the 
extraction of the roots of high powers ; and attempted to point 
out an improved method of effecting that difficult task ; but the 
nature of the communication did not admit of its being read in 
adletail. 
Feb. 11.—A paper, by Capt. J. Ross, R. N. was read, on the 
variation of the compass. The variation of the compass was one 
of the objects that particularly engaged the author’s attention 
during his late voyage to the Arctic Regions; and he detailed 
his experiments on this subject in the order in which they were 
made. From these he concluded, that every ship has a peculiar 
attraction affecting her compasses, the exact amount of which 
it is difficult to ascertain. This attraction is not progressive, but 
irregular, and scarcely admits of general rules; .and hence the 
rules usually given on the subject are not to be depended upon, 
especially in very high latitudes. In the Isabella, six compasses 
were found to agree when in the same place; but they all dis- 
agreed when removed to different situations between the stern 
and foremast. Hence the variation of the compass will differ 
according to the place it occupies im the ship. The time of 
