46 Spirit of Philosophical Discovery. 
interesting experiments are contained in 
three tables, printed in No. xxiv. of 
Jameson’s Edin. Phil. Journal: from these 
it appears, that a compas fixed in the fore- 
part of the vessel, fifteen feet eight inches 
from the large chimney, when the vessel’s 
head was N.E., shewed a deviation west- 
ward of 12°31’, and when the head was 
nearly W. an eastward deviation of 15° 50’, 
Fortunately, however, it appeared, that, at 
the binnacle or place of the steering com- 
pass, the greatest deviations observed were, 
3° 55’ westward, with the head near east, 
and 3° 20/ eastward, with her head nearly 
west. So accurately now is the principle 
of local attraction in a vessel known to Mr. 
Barlow, that he was able, before beginning 
to observe the compass’s bearings, to select 
a spot on the deck, at seven feet eight 
inches distance from the binnacle, where 
the action of the iron below was so exactly 
balanced by that of the chimnies above, as 
to leave a standard compass erected on this 
spot, very nearly as correct in all its bear- 
ings, as if no causes of local attraction had 
been present. 
The Alteration in the Magnetism of an 
Tron Body, occasioned by Rotation on an 
Azis, has been the subject of two elaborate 
series of experiments, communicated lately 
to the Royal Society, viz. by Mr.P. Barlow, 
who operated on a cast-iron shell, of con- 
siderable thickness, mounted on the maun- 
drel of a Jathe, and made to revolve on its 
axis ; and by Mr. S.H. Christie, who caused 
an iron plate to revolve in its own plane ; 
and in each instance, striking effects were 
noticed, on magnetic needles, different from 
what the same iron bodies in a state of rest 
would have occasioned, causing them to 
deviate from the magnetic meridian: ac- 
cording as the bodies revolved, towards or 
from the needles, the latter were attracted 
orrepelled. The germs of some important 
discoveries relative to terrestrial magnetism 
seemed partially developed by these experi- 
ments; but very lately, Messrs. C. Babbage 
and J. F. Herschell haye expressed an opi- 
nion to the Society, that the effects may be 
explained, by supposing, simply, that time 
is requisite, both for the development and 
the loss of magnetism: and from their own 
experiments, on setting in horizontal rota- 
tation a powerful horse-shoe magnet, and 
suspending freely over it, successively, 
masses of copper, zinc, silver, tin, lead, 
antimony, mercury (in a glass tube), gold, 
bismuth, and a metalloid of carbon, all of 
which were found to acquire motion, and 
to follow the magnet, they conclude, that 
different metals differ in respect, not only 
of the time they require, but in the intensity 
of the force ultimately producible in them. 
The brevity of the notices published, leave 
us to conjecture the influence which cur- 
rents of air, generated by the revolving 
body or magnet, may or may not have had, 
in producing the effects noticed. Before 
our next publication, we hope these doubts 
[Aug. I, 
will be cleared up, by fuller statements, 
and by new and yaried experiments. 
An Analogy between the Brain, Ova and 
Semen of animals, has lately been shewn by 
Sir E. Home, aided by the acute eye and 
delicate hand of Mr. Baucer, in that freez- 
ing and subsequent thawing these sub- 
stances resolves them into apparently simi- 
lar watery fluids and gelatinous matters. 
The Dependence of Perceptions by the 
Senses on Muscular Exertion, particularly 
as concerns vision, has been the subject of 
several papers presented lately to the Royal 
Societies of London and Edinburgh, by 
Mr. C. Bell; who maintains, that not only 
are our ideas formed by a comparison of 
the different signs presented to us through 
the senses; but there is a power in the 
body, which, though not called a sense, is 
superior to all the senses, in the precision 
which it gives to our perceptions—bestow- 
ing on ws accurate ideas of distance, of 
space, of form and substance ;—that the 
muscular frame, and that sense which we 
possess of the muscular frame in action, 
gives us this power;—that the sense of 
vision in the eye is imperfect, until aided 
by muscular motion: as the sense of touch 
in the hand would inform us of nothing, 
without the motions of the hand ;—that 
hardness, softness, smoothness and angu- 
larity are properties of matter, not known 
to us merely by the sense of touch, but by 
that sense, aided by the motions of the 
hand—of which motions we are sensible ;— 
that the entire and complete exercise of 
the sense of touch comprehends a compari- 
son of the exercise of the nerve of touch 
with the consciousness of, or the sensibility 
to, the muscular motion which accompanies 
it. On viewing an object which is very 
suddenly withdrawn, the image or phantom 
in the eye is stationary, whilst the eye-ball 
is at rest; but the slightest exertion of the 
voluntary muscles of the eye makes a 
change in the apparent position of that 
image, whilst actually it is fixed on the 
same spot of the retina. The eye, with 
its apparatus of muscles, has the power of 
conveying the idea of the phantom in dif- 
ferent positions, according to the operations 
of its muscles, and independent of the 
motions of the head or body. 
Seeing Objects under Water.—The con- 
troverted opinion, as to whether this is 
practicable or not, has been revived, in 
Jameson’s Journal, without any new light 
being thrown upon it; although nothing is 
more easy or safe, than for any one to 
make the experiment for himself. Nearly 
fill a wash-hand basin with clear water, to 
which a small proportion of warm water 
may be added, if the weather be cold; and 
then, holding the breath, dip the face into 
the water, two or three inches deep, and 
hold it there, as long as the want of breath- 
ing will permit; when it will be found that 
the eyes can be opened and shut under 
water, 
