The Liverpool Standard and General Commercial Advertiser.
Liverpool, Merseyside, England, 1841-04-16 00:00:00

SHIPMASTERS' ASSOCIATION

One of the most entertaining and useful lectures we have
ever listened to was given by Mr. Purnell, at this rising in-
stitution, on Monday evening last. The subject was Mental
Nautical Astronomy, which, as described
.by the lecturer,
is an exceedingly ingenious way of working astronomical pro-
blems, without the aid of pen, book, dr map : and when it is
considered that the mariner is often unable to obtain these
helps when most anxious to ascertain his position, the sub-
ject assumes an importance and value which cannot be too
strongly impressed upon nautical men. Previous to the
opening of the lecture, Mr. Rowatt addressed the company,
and st‘ted that lie had studied the science under Mr. Pur-
nell some years ago, and could bear the strongest testimony
to the great utility of it from his own experience. He felt,
therefore, the greater pleasure in introducing that gentleman,
who had so handsomely responded to the call made upon him
al the close of Mr. Hunt's last lecture, and whose reputation
for thorough knowledge of the subject about to be brought
forward was so well known.
Mr. Purnell commenced his address by a modest and elo-
quent appeal to his hearers on behalf of his favourite study,
and then proceeded to expound the system in detail. Our
limits will not allow us to follow the talented lecturer so
much at length as we could wish, and we must content our-
selves with a brief sketch of its leading features. Mental
nautical astronomy is founded upon mnemonics, the nume-
rals being represented by the consonants of our alphabet. A
student is supposed to place himself in the centre of a square,
or four-sided room. He draws an imaginary line round the
middle of the walls, and considers the space above the line
as the northern, and the space below as the southern hemi-
sphere. Each wall comprehends a season in annual calcula-
tions, six hours in daily reckoning, and ninety degrees in the
earth's measurement. Along the equinozial line the mind
places the twelve signs of the zodiac, three on each wall, and
by associating some pictorial association with their names,
they are easily and firmly fixed in the memory. In like man-
ner, by a longitudinal and horizontal subdivision of the walls
nto imaginary spaces, and placing the fixed stars, in their
pictorial character, within them, the mind soon acquires a
recollection of their positions which, in the ordinary way, is
rarely completely mastered. The calculations of the appa-
rent movement of the sun and fixed stars in the heavens,
caused by the motion of our earth, are then carried on by
means of short pithy sentences, containing the consonants,
which give the results sought for ; and the right ascension of
the sun on any given day, the hour any star passes the meri-
dian, or, in fact, any problem of calculation in astronomy, is
arrived at by this method in a manner surprisingly rapid and
easy, as was demonstrated by the quick replies the lecturer
elicited from his auditors, some of whom, to our knowledge,
had never heard of the system previously, and all of whom
were certainly at that moment deprived of the aid of their
old friend Norie. Tyros in astronomy were amazed at find-
ing themselves, in the space of a few minutes, capable of cal-
culating movements of heavenly bodies, the mere names of
which they were scarcely acquainted with before, and not a
few of the veteran commanders made up their minds (if we
mistake not) to remedy the neglects of early education, by
studying this rail-road key to that all-important science
which opens to the mariner the ends of the earth, and enables
him to steer his bark in safety over the pathless deep !

At the conclusion of the lecture the audience testified their
high sense of Mr. Purnell's abilities, and of the entertain-
ment and instruction he had given them, by loud and conti-
nued plaudits. A vote of thanks was unanimously passed,
accompanied by a request that he would not only continue
the subject at a future day, but that he would repeat the lec-
ture of that evening at an early period, in order that they
might have the pleasure of hearing it again, and be enabled
to afford their friends the benefit of the whole series, by at-
tending at the repetition. Mr. Purnell, with that generous
disregard of time and trouble which characterises the man of
genius and learning, most kindly, and without hesitation,
assented to the wishes of the company, and promised to
" begin again" o❑ Monday evening next, at half-past six in
the evening, when we shall be much surprised if the room of
the association will contain the candidates for admission.

The oldest bridge now existing in England is the triangular
bridge at Croyland,in Lincolnshire, (sometimes called Crow-
land) which is said to have been erected about A.D. 860, but
with what view it is difficult, if not altogether impossible to
determine. It is obvious that utility was not the object of the
builder, though it may be allowed to claim the qualities of
boldness of design, and singularity of construction, as much
as any bridge in Europe. It is formed by three semi-arches,
whose bases stand in the circumference of a circle, equidis-
tant from each other, and uniting at the top. Nicholson
says that this curious triune formation has led many persons
to imagine that the architect intended to suggest an idea of
the Trinity thereby. This venerable bridge is now nearly
1,000 years old !

CAMBRIDGE.—BEAUTIFUL WORKING OF THE POST-
OFFlCE.—Considerable excitement has for some time past
prevailed, owing to a number of letters and newspapers not
having reached the hands of the parties to whom they had
been addressed ; and on Friday suspicion having fallen upon
William Jervis, one of the letter carriers in this town, the
superintendent of police and an officer searched his dwelling-
house, where they discovered 261 letters and 74 newspapers,
all of which had been embezzled ; and on apprehending him
in the afternoon 41 letters were found on him which should
have been delivered in the morning. Information having
been given to the mayor, Jervis was examined, and remanded
for further examination till Friday next, to allow time for the
Postoffice authorities to come forward to prosecute. On
being taken to the gaol and searched by the gaoler, four other
letters were found secreted on his person, one of which, at
least, was a money letter.—Cambridge Advertiser. •