

TRANSACTIONS OF THE SECTIONS. 11 
places of observation where there would be no deviation while the ship’s head re- 
mained in the same direction. : 
. This position I practically discovered by moving the compass a few inches at a 
time, till it indicated the correct magnetic direction of the ship’s head. 
The question which now remained to be proved, was, to what extent the deviations 
of the said compass had been iessened (or what they actually were) when the ship’s 
head was placed upon different points, and I was gratified to find that after swing- 
ing the vessel and observing upon the eight principal points, the compass, placed as 
before described, proved to be correct within + of a point. 
It is necessary to mention that the “Trident”? has wooden beams under the 
quarter-deck, and therefore it remains to be seen to what extent such observations 
may be useful in vessels which have iron beams. 
It will also be requisite to ascertain by actual observation how far a position so 
selected shall prove advantageous when the ship changes her geographical position ; 
and as the ‘‘ Trident” is about to proceed to the southern hemisphere, and is amply 
provided with instructions and the means of ascertaining such changes, and as I 
shall swing her again at Greenhithe on every point before she leaves, we may hope 
for much useful information on this important subject. 
In sending you these remarks, I must observe, that it may not always be practi- 
cable to find the position of no-deviation, or where the influences of the iron in the 
ship upon the magnetic needle are equalized, because such a point might be found in 
a most inconvenient position, or be too near moveable iron work, machinery, &c.; 
but if we succeed in approximating towards it, and thereby reduce the deviations 
within moderate limits, a point of great practical importance will be gained in navi- 
gation. 
On a peculiarity of Vision. By Professor Powe, F.R.S. 
‘The peculiarity to which I refer affects both my own eyes, but more especially the 
left eye. They have always been long-sighted, but I never used glasses till about 
seven years ago. About that time I had, I fear, injured my eye-sight generally by 
optical experiments, and have in consequence thought it prudent to desist from them 
ma great degree. I then perceived a general indistinctness of vision, which is how- 
ever completely removed by the use of convex glasses of long focus ; but I have not 
till lately been aware of the precise nature of this indistinctness. I have now found 
that it is produced by the image of every small object, as for instance, a fine dark line 
on a white ground appearing TRIPLE. I do not find any difference from varying 
the distance of the object from the eye, nor in placing the line in different azimuths 
round the axis of the eye; the appearance is presented whether I use one eye or 
both, but is somewhat less marked with the right eye. Conjectures may easily be 
started as to the change of form in the lens which might produce such an appear- 
ance, but I wiil not at present do more than simply mention the fact, as it may 
perhaps elicit other statements of a similar kind which may tend to throw light on 
the question as to its nature. 
On Luminous Beams. Communicated by Professor PowE.., F.R.S. 
Appearances of luminous beams in the sky, of a peculiar kind, agreeing neither 
with the characteristics of aurora, nor of the zodiacal light, have been occasionally 
recorded. A remarkable instance of this kind was observed by Mr. G. A. Rowell, 
at Oxford, July 11, 1850 :—** When the sun was just setting, or set, but hidden by 
clouds, he saw a bright beam with parallel sides extending vertically upwards from’ 
the place of the sun to an altitude estimated at 15° or 20°.”” Again, on July 6, 1852, 
Mr. Rowell saw a similar phenomenon which he describes thus :—‘‘ About 10 o’clock 
p.m., I observed two extraordinary rays of light in the N.N.W., each extending 
from the horizon to upwards of half-way towards the pole star, and apparently pro- 
ceeding from the sun’s place below the horizon, in a direct line towards that star. I 
watched this phenomenon till 10" 30", and I believe it could not have been caused 
