T I M 
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|p wheel is one ; but in this time-keeper the 
(heels have only about one-eightieth part of 
je power over the balance that the balance- 
Iring has; and it must be allowed, the less 
|e wheels have to do with the balance, the 
letter. The wheels in a common watch 
Iving this great dominion over the balance, 
ley can, when the watch is wound up, and 
pe balance at rest, set the watch a going ; 
ut when my time-keeper’s balance is at rest, 
hd the spring is wound up, the force of the 
Teels can no more set it a going than the 
'heels of a common regulator can, when the 
'eight is wound up, set the pendulum a 
ibrating ; nor will the force from the wheels 
love the balance when at rest, to a greater 
ngle in proportion to the vibration that it is 
i fetch, than the force of the wheels of a 
ommon regulator can move the pendulum 
“orn the perpendicular, when it is at rest. 
“ My time-keeper’s balance is more than 
iree times the weight of a large-sized com- 
1011 watch balance, and three times its dia- 
leter; and a common watch balance goes 
prough about six inches of space in a second, 
jut mine goes through about twenty-four 
aches in that time ; so that had my time- 
eeper only these advantages over a common 
'atch, a good performance might be expect- 
d from it. But my time-keeper is not affect- 
'd by the different degrees of heat and cold, 
tor agitation of the ship ; and the force from 
he wheels is applied to the balance in such a 
planner, together with the shape of the ba- 
mce-spring, and, if I may be allowed the 
erm, an artificial cycloid, which acts at this 
ring ; so that from these contrivances, let 
e balance vibrate more or less, all its vibra- 
ions are performed in the same time ; and 
herefore if it goes at all, it must go true. So 
hat it is plain from this, that such a time- 
:eeper goes entirely from principle, and not 
com chance.” 
We must refer those who may desire to see 
. minute account of the construction of Mr. 
larrison’s time-keeper, to the publication 
•y'order of the commissioners of longitude. 
We shall here subjoin a short view of the 
improvements in Mr. Harrison’s watch, from 
he account presented t® the board of .longi- 
ude by Mr. Ludlarn, one of the gentlemen 
o whom, by order of the commissioners, Mr. 
larrison discovered and explained the prin- 
ciple upon which his time-keeper is con- 
tructed. The defects in common watches 
jrhich Mr. Harrison proposes to remedy, are 
diiefly these : 1. That the main spring acts 
lot constantly with the same force upon the 
vheels, and through them upon the balance. 
J. That the balance, either urged with au 
mequal force, or meeting with a different re- 
istance from the air, or the oil, or the fric- 
ion, vibrates through a greater or less arch. 
|. That these unequal vibrations are not 
icrformed in equal times. And, 4. That the 
orce of the balance-spring is altered by a 
Tange of heat. 
To remedy the first defect, Mr. Harrison 
ias contrived that his watch shall be moved 
iy a very tender spring, whwh never unrolls 
tself more than one-eighth part of a turn, 
iiid acts upon the balance through one wheel 
jiily. But such a spring cannot keep the 
vatch in motion a long time. He has, there- 
ore, joined another, whose office is to wind 
jp the- first spring eight times in 'every mi- 
juffl, and which is itself wound up but ©nee a 
; Vo l . II. 
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day. To remedy the second defect, he uses 
a much stronger balance-spring than in a 
common watch. For if the force of this 
spring upon the balance remains the same, 
whilst the force of the other varies, the errors 
arising from that variation will be the less, as 
the fixed force is the greater. But a stronger 
spring will require either a heavier or a larger 
balance. A heavier balance would have a 
greater friction. Mr. Harrison, therefore, 
increases the diameter of it. In a common 
watch it is under an inch, but in Mr. Harri- 
son’s, two inches and two tenths. However, 
the methods already described only lessening 
the errors, and not removing them, Mr. Har- 
rison uses two ways to make the times of the 
vibrations equal, though the arches maybe 
unequal : one is to place a pin so that the 
balance-spring pressing against it, has its force 
increased, but increased less when the varia- 
tions are larger; the other, to give the pallets 
such a shape, that the wheel may press them 
with less advantage when the vibrations are 
larger. To remedy the last defect, Mr. 
Harrison uses a bar compounded of two thin 
plates of brass and steel, about two inches in 
length, riveted in several places together, 
fastened at one end, and having two pins at 
the other, between which the balance-spring 
passes. If this bar is straight in temperate 
weather (brass changing its length by heat 
more than steel), the brass side becomes con- 
vex when it is heated, and the steel side when 
it is cold ; and thus the pins lay hold of a dif- 
ferent part of the spring in different degrees 
of heat, and lengthen or shorten it as the re- 
gulator does in a common watch. 
The principles on which Mr. Arnold’s 
time-keeper is constructed are these: The 
balance is unconnected with the wheel-work, 
except at the time it receives the impulse to 
make it continue its motion, which is only 
whilst it vibrates 10° out of 380°, which is 
the whole vibration ; and during this small 
interval it has little or no friction, but what 
is on the pivots, which work in ruby holes on 
diamonds. It has but one pallet, which is a 
plane surface formed out of a ruby, and has 
no oil on it. Watches of this construction, 
says Mr. Lyons, go whilst they are wound 
up ; they keep the same rate of going in every 
position, and are not affected by the different 
forces of the spring; and the compensation 
for heat and cold is absolutely adjustable. 
TIN, a metal known to the antients : the 
Phenicians procured it from Spain and Britain, 
with which nations they carried on a very 
extensive and lucrative commerce. This 
metal has a fine white colour, like silver ; a 
slight disagreeable taste, and emits a peculiar 
smell when rubbed. Its specific gravity is 
729. It is very malleable. Tin-leaf or foil 
is about tb part of an inch thick, and it 
might be reduced to half this thickness. It 
is very flexible, and produces a remarkable 
crackling noise when bended, and when heat- 
ed to 442° it melts. When exposed to the 
air it very soon loses its lustre, and assumes a 
greyish-white colour, but undergoes no far- 
ther change. Neither is it sensibly altered 
by being kept under cold water; but when 
the stream of water is made to pass over red- 
hot tin, it is decomposed, the tin is oxidated, 
and hydrogen gas is evolved. 
When tin is melted in an open vessel, its 
surface becomes very soon covered with a 
5 1 
»• 
80 1 
grey powder, which is an oxide of the metal. 
If the heat is continued, the colour of the 
powder gradually changes, and at least it be- 
comes yellow, in this state it is known by 
the name of putty, and employed in polishing 
glass and other hard bodies. When tin is 
heated very violently in an open vessel, it 
takes fire, and is converted into a fine white 
oxide, which may be obtained in crystals. 
Tin is capable of combining with two dif- 
ferent proportions of oxy gen, and of forrhing 
two oxides ; usually distinguished, on account 
of their colour, by the names of the yellow 
and the white oxide. 
The protoxide may be obtained by ex- 
posing tin to a strong heat under a muffle, 
constantly stirring it with a rod. It may be 
procured also by dissolving tin in diluted 
nitric acid without the assistance of heat, and 
then precipitating the oxide by pure potass ; 
but in that case it retains a little acid, and 
has a white colour. It is composed of about 
20 parts of oxygen and 80 of tin. 
The peroxide may be obtained by beating 
tin in concentrated nitric acid. A violent 
effervescence ensues, and the whole of the 
tin is converted into a white powder, which 
is deposited at the bottom of the vessel. It 
is composed of about 28 parts of oxygen and 
72 of tin. 
Tin combines with sulphur and phospho- 
rus ; but it lias never been combined with 
carbon or hydrogen . 
Sulphuret of tin may be formed by throw- 
ing bits of sulphur upon the metal melted i* 
a crucible, or by fusing the two ingredients 
together. It is brittle, heavier than tin, and 
not so fusible. It is of a blueish colour and 
lamellated structure, and is capable of cry- 
stallizing. According to Bergman, it is com- 
posed of 80 parts of tin and 20 of sulphur ", 
according to Pelletier, of 85 parts ot tin and 
1 5 of sulphur. 
When equal parts of white oxide of tin and 
sulphur are mixed together and heated gra- 
dually in a retort, some sulphur and sulphu- 
rous acid are disengaged; and there remains 
a substance composed of 40 parts of sulphur 
and 60 of white oxide of tin, formerly called 
aurum musivum, musicum, or mosaicum, and 
now sulphureted oxide of tin. It consists of 
beautiful gold-coloured flakes, exceedingly 
light, which adhere to the skin. r l lie pro- 
cess for making this substance was formerly 
very complicated. Pelletier first demon- 
strated its real composition, and was hence 
enabled to make many important improve- 
ments in the manner ot manufacturing it. 
Phosphuret of tin may be formed by melt- 
ing in a crucible equal parts of filings ot tin 
and phosphoric glass. 1 in has a greater affi- 
nity for oxygen than phosphorus lias. Part 
of the metal therefore combines with the 
oxygen of the glass during the fusion, and 
flies off in the state of an oxide, and the rest 
of the tin combines with the phosphorus. 
The phosphuret of tin may be cut with a 
knife; it extends under the hammer, but se- 
parates in laminae When newly cut, it has 
the colour of silver ; its filings resemble those 
of lead. When these filings are thrown on 
burning coals, the phosphorus takes fire. 
This phosphuret may likewise he formed hv 
dropping phosphorus gradually into melted 
tin. According to Pelletier, to whose expe- 
riments we are indebted for the knowledge of 
all the phosphurets, it is composed of aboufc 
