1825.] [ 45 
SPIRIT OF PHILOSOPHICAL 
VARIOUS SCIENT 
] 
DISCOVERY, AND OF THE 
IFIC JOURNALS. 
—<=z_———- 
TSHE Southern Motion of some of the 
fixed Stars, for which, as yet, no 
cause has been assigned by physical astro- 
nomers, is still contended for by Mr. Pond, 
notwithstanding the opposition his former 
statements, on this head, received from 
numerous astronomers ; this he has lately 
done, by presenting to the Royal Society 
a table of Dr. Brinkley’s (Dublin) obser- 
vations on sixteen stars, near half of which 
shew, Mr. P. says, a greater annual de- 
viation southward, than he (Mr. P.) con- 
tends for ; and all but three of these stars 
either shew such deviation, or, at least, are 
not inconsistent with it; Dr. B.’s three 
other stars indicate a northern deviation. 
On determining the Direction of the Meri- 
dian of observatories. Two papers have 
lately been read before the Royal Society : 
one by Professor Woodhouse, detailing the 
obstacles met with, and the mode ot ob- 
viating them, cccasioned by temporary ex- 
- pansion in the metallic supports of the 
transit instrument of the new Cambridge 
Observatory, whilst fixing its southern 
meridian mark on Granchester Steeple, 
about two miles distant; the other by Mr. 
Pond, who proposes a telescope mounted 
on a horizontal axis, or a transit instru- 
ment, to be, in the first instance, directed 
to the greatest elongation westward of the 
pole star; an artificial horizon to be, at the 
same time, ready for viewing the star, by 
reflection, through the telescope ; and, also, 
at a proper and convenient distance, the 
farther oif the:better, a graduated horizon- 
tal bar, properly illuminated, to.be tem- 
porarily fixed, in the telescope’s field of 
view: then, immediately after observing 
the star’s greatest elongation, the telescope 
is to be lowered to observe and note the 
graduation on the bar, and then further 
lowered to observe the reflected image of 
the star, as a check on the verticity of the 
plane, which the central wire has _tra- 
versed, between the star and its image. 
When, by repeating these operations, a 
point is ascertained, and a staff erected in 
place of the graduated bar, the same is 
then to be removed (unless for greater ex- 
pedition two such are used) to 2 convenient 
place in tie vertical plane of the pole-star’s 
yreatest eastern elongation, and the same 
operations repeated as before; the middle 
point, then, between these two polar elon- 
gation-staves, will lie in the northern meri- 
dian of the telescope ; and the latter distance 
may be bisected, by careful horizontal mea- 
surements between the staves, checked by 
angular measurements. It might be well 
that astronomers should ascertain, and per- 
_manently preserve elongation marks, as 
well as meridian marks, adapted to occa- 
sional azimuthal checks on the positions of 
their instruments. 
It is a point of great importance in con- 
ducting the trigonometrical survey of a 
country, to ascertain correctly the direction 
of the meridian, at each station: for which 
purpose this mode, suggested by Mr. 
P. seems very applicable; and, we ven- 
ture to suggest, in the government survey, 
which is now commencing in Ireland, 
that, before the great Theodolite visits 
each station, to observe the horizontal 
angles, a good portable transit instrument, 
and party of surveyors, should, on the spot, 
select the site of the station, and fix up its 
elongation staves, at proper distances, north- 
ward, after very careful, and often-repeat- 
ed observations, as above mentioned; in 
order that the bearings of these staves, may 
be settled by the great Theodolite, with 
equal accuracy as the surrounding stations. 
In England, a private of artillery, sent for- 
wards on foot, with a small telescope in his 
pocket, selected the sites, and fixed up 
marks for most of the stations: whence 
delays and many inconveniences followed, 
which now may be avoided. 
Whether the Earth possesses two or four 
Magnetic Poles is a disputed point, which 
Professor Hansteen proposes to clear up, 
by making a journey into Siberia, to search 
for, and ascertain the exact site of the mag- 
netic pole, there alleged to be situated ; 
or, at any rate, by a careful and extensive 
series of experiments on the variation and 
dip of the needle, and the magnetic inten- 
sity in that inhospitable region, to furnish 
useful dafa for magnetic investigations : 
also, by pendulum observations, combined 
with astronomical observations, to supply 
some much-wanted data, as to the figure 
of the earth, and the position of places 
thereon: the climate, natural productions, 
&c. not to be overlooked; the King of 
Sweden patronizes this journey, intended 
of two or three years’ duration. 
The Local Magnetic Attraction in Steam- 
Vessels, owing to the greater quantity of 
iron in their construction, and the different 
distribution thereof, from other vessels, in 
their boilers and engines below, and their 
iron chimnies for smoke and waste steam 
above the deck, has occasioned Government 
to employ Mr. Barlow, with the assistance 
of six of the most advanced of the pupils 
of the Royal Naval Architectural College 
at Portsmouth, to experiment fully on the 
deviations of compasses, differently situated, 
on board of the Comet steam-vessel (of 
237 tons burthen, Jength 115 feet, and 
breadth twenty-one. tat), with her head in 
all different positions, with respect to the 
magnetic meridian, ‘The details. of . these 
interesting 
