1824.] > 
each evening, according to the greater or 
less number of chronometers that may want 
comparing, and the number of repetitions 
of observations for each, which it may be 
found necessary to provide for. On board 
the ships the chronometers will best be 
compared in the cabin, where they are kept, 
by an observer watching the progress of 
the second-hand, until the instant that a 
person over-head on the deck stamps with 
his foot, as a signal that the observatory 
light has disappeared. or greater security 
against mistakes of 5m., or of any other 
constant distance of time, at which the lamp 
might be hid from view, it might be well to 
use three different intervals, viz. 4m, 5m, 
and 6m. between the darkening signals ; 
that is, to obscure the lamp at Om, 4m, 
9m, 15m, 19m, 24m, 30m, &c. of the 
clock. 
Improvements in Naval Architecture engage 
the sedulous attention of the present Lords 
of the Admiralty. ‘Three new sloops of 
war, the Orestes, Phylades, and the Cham- 
pion, each constructed and rigged accord- 
ing to the plans of as many projectors of 
improvements in naval tactics, arrived at 
Spithead on the 3d of November, after an 
experimental cruise from Torbay; the lat- 
ter of these vessels, on the plan of Captain 
Hayes, having been found decidedly the 
superior in nearing the wind, possessing, at 
the same time, far the greatest stowage-room, 
and having been proved to strain the least 
in bad weather. Further comparative trials 
of the sloops are, however, intended, after 
the two former have been docked, and un- 
dergone those repairs and alterations which 
are judged necessary by their projectors, 
but.of which the latter sloop is thought. to 
stand in no need 
Ship-building without Ribs.—The City of 
Rochester East Indiaman, of about 600 
tons burthen, Jately launched from the 
yard of Messrs. Brindley and Co. at Ro- 
ehester, but built by Messrs. Macqueen 
and Palmer, has her bottom and sides con- 
sisting wholly of planks, in separate thick- 
nesses, worked fore and aft; the planks of 
one thickness covering the joints or seams 
ef the other, alternately. Under the last 
coating or outside planking, hoop-ribs of 
iron are let in, at proper distances, crossing 
at right angles the planking of the bottom, 
sides, and deck; and these hoops, being 
firmly secured inside the ship by secrew- 
nuts, the whole is combined in the strongest 
manner possible, 
Reflecting Mirrors for Naval Light-houses, 
were the invention of Captain Hutchinson, 
dock-master at Liverpool, who, in 1763, 
erected there (the first which were in use) 
small ones of tinned plate, soldered toge- 
ther; and larger ones, as far as twelve feet 
diameter, of wood, lined with numerous 
plates of looking-glass. 
Professor Barlow's Corrective of the Local 
Attraction on a Ship's Compass, which con~. 
Spirit of Philosophical Discovery. 
437 
sists in the admirably simple expedient of 
placing a flat round plate of iron in such 
a fixed position, near to a ship’s compass, 
that its attraction on the needle shall, in 
every possible position of the ship’s head,’ 
exactly correct the great and uncertain 
deviation from the magnetic meridian, which’ 
the iron materials and utensils on ‘board 
would otherwise occasion, is coming fast 
into use, not in this country only, but in’ 
the Russian and other foreign navies. — As 
expressive of the sense which the Trinity’ 
Board entertain of the great value of Mr. 
Barlow’s discovery, they have lately pre- 
sented him with £200, accompanied by a 
most flattering letter. In the road of Cron- 
stadt, Admirals Heyden and Krusenstern, 
of the Russian navy, experimented upon 
one of Barlow’s compasses, “ made by’ 
Messrs. Gilbert, and found the deviation 
thereby corrected, within a quarter ofa de-» 
gree, on every position of the ship’s head. — 
Phil. Mag. No. 318. ; 
That the Diurnal Variation of the Magnetic’ 
Weedle becomes nothing on the Magnetic Bqua- 
tor, has been inferred by M. Arago, from am 
extensive series of observations on the mag-> 
netic variation made by M. Duperrey, and: 
submitted to him for examination. 
The Electro-magnetical Experiments of Mr. . 
William Sturgeon of Woolwich, detailed in . 
numbers 312 and 318 of the “ Philosophi- 
cal Magazine,” shew, that a magnetic bar, - 
mounted freely on an axis passing through 
its two poles, and in this state subjected to’ 
currents of electricity, passing from its 
equator or middle point towards each pole,* 
is thereby caused to revolve on its axis; so’ 
also, if the magnet be fixed, and a system 
of wires connected like the meridians’on a* 
globe, be freely mounted on an axis, pass-— 
ing through the magnet’s poles, and the 
wires be electrified from the equator to? 
each pole: im such case, the system of 
wires will revolve round the magnetic axis. - 
From whence Mr. Sturgeon seems almost 
disposed to reyive the hypothesis of Dr.. 
Halley, who supposed the earth to contain 
a spherical magnet, which rotated within 
the shell which we inhabit! At the same 
time that he (Mr. S.) indicates an inge- 
nious, and far more probable , hypothesis, 
viz. that the solar heat, acting principally. 
on the equatorial parts of the earth, gene- 
rates there vast quantities of the electrical ’ 
fluid, which flow continually and equally 
towards each of the poles of the earth ; ac-’ 
cording to which, if the earth constituted a 
vast magnet, the results of his experiments 
(alluded to above) would shew the proba-' 
bility, that the diurnal rotation of the earth, — 
and also the constant parallelism of its axis, 
might be accounted for. 
The Glow-worm shines more intensely in 
Oxygen Gas than in atmospheric air, not be- 
cause an actual combustion of its luminous 
parts takes place, but because of the stimu- 
lus which the oxygenous gas presents fi 
the 
