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the most powerful receiving and retaining the virte
stone ; he also affirms that he has fully satisfied
infuse such virtue into a piece of steel, that
of iron of two ounces weight or more ; ar
the virtue of conforming to the magnet
help of a loadstone or any thing
therefrom.

ON MAGNETISM.

*16. Troy.

1402. I dut, lifted by
witte brass, suspended by a
ght, and 4-10ths of an inch in
a parallelopiped form, almost four

zbing all together 1 oz. 14 dwt. lifted
gpped or armed with iron at each end,
..Ost of the same form as the last, but only

weighing 2 oz. 8; dwt. lifted by one of its ends

tried, consisting of

be feet

for tho

2. By Mr. (afterwards Dr.

Royal Societe
Mr. Knight, of Magda'
a meeting of the Royal
ber, 1744, produced
curious artificial m
consisted of plain
of the same sub
of natural loar

to his study; before made

uwed that the poles were of lifting

at the same end, which before at. advantag

the needle, now attracted the north, and

and vice versa. at his atr. Knight, again taking the stone, brought it back the. a time as before, with the direction of its polarity turo.

ight angles to its former direction, and into the direction of 3 natural grain of the stone, the poles now lying in the flat ends of the cylinder; one of which, being the smoother end, attracted the south end of the needle, while the other, which was of a rooster texture, attracted the north end, and repelled the south end of the same : when it was also observed, that the polarity appeared stronger in this case, than either of the former.

Lastly, Mr. Knight, in about the same time, inverted this last direction of the poles, keeping it still parallel to the axis of the cylinder, but causing the smooth end of the stone to attract the north end of the magnetic needle, and the rough end to attract the sonth, and repel the north end of the same needle.

After this report, Mr. Knight proceeded to show, at the meet. ing, some of the same artificial magnets there mentioned; and it was found, that the compound magnet, consisting of twelve steel bars, and which had, in the experiinent made before the president,

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ON MAGNETISM.

21 oz. Troy weight, did here, under all the inconve.
isadvantages of a crouded room, still lift a weight
Ib. 11 oz.
d, that the single armed block of steel, which
'h. 2 oz. did here, under the same disadvan.

13 lb. 7 oz.
ht produced to the company the above.

belonging to Mr. Hauksbee, but with
in altered from what it was, when it

weighing 2 oz. 84 dwt. lifted by one of its ends

·ll together 1 oz. 14 dwt. lifted

or armed with iron at each end, of the same form as the last, but only

pended by a Cths of an inch in ved form, almost four

989

ifted by

ts mentioned in the foregoing

others to be made of a less and one of these, weigh

and with the armour,

jo oz.

of steel, each two inches suth, and not above 6.100ths of an were laid flat on each other, and screwed wall brass screws going through the three plates, -.1, the little parallelopiped block so made up, was armed tron at the two ends, cramped together with silver, and fitted with a double ring of the same metal, for the convenient holding of it.

[Phil. Trans 1744.

3. By Mr. Benjamin Wilson.

Containing an account of Dr. Knight's method of making artificial Loadstones.

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The method was this: having provided himself with a large quan. tity of clean filings of iron, Dr. K. put them into a large tub that was more than one-third filled with clean water; he then, with great labour, worked the tub to and fro for many hours together, that the friction between the grains of iron by this treatment might break off such smaller parts as would remain suspended in the water for some time : the obtaining of which very small particles in sufficient quantity seemed to him to be one of the principal desi. derata in the experiment. The water being by this treatment ren. dered very muddy, he poured it into a clean carthen vessel, leaving the filings behind; and when the water had stood long enough to took op distinctly, with the same apparatus as before, 6 oz. 18 dut. 3 gr. ; since which time it has also several times been found to lift nearly the same quantity.

Mr. Knight further, at the same time, showed the president the following instances of his ability to invert or change the direction of the poles in natural loadstones.

Such a stone belonging to Mr. Francis Hauksbee, weighing about 5 oz. 14 dwts, of an irregular cylindrical form, with two of the sides somewhat fatted, on which armour had formerly been ap. plied, had the direction of its polarity from one of these fatted sides to the other, notwithstanding the stone had a distinct grain running at right angles to that direction. It was tried, and observed that one of these flatted sides strongly attracted the north end, and repelled the south ; and that the other attracted the south, and repelled the north end of the magnetic needle. The end of the stone, attracting the south end of the needle, was then marked, by the rubbing of a piece of silver upon it, as on a touchstone: after which, Mr. Knight carried the stone into his study; and reproducing it in about a minute, showed that the poles were then directly inverted; and that the same end, which before attracted the south end of the needle, now attracted the north, and repelled the south, and vice versa.

After this, Mr. Knight, again taking the stone, brought it back in as short a time as before, with the direction of its polarity turn. ed at right angles to its former direction, and into the direction of the natural grain of the stone, the poles now lying in the flat ends of the cylinder ; one of which, being the smoother end, attracted the south end of the needle, while the other, which was of a rougher texture, attracted the north end, and repelled the south end of the same : when it was also observed, that the polarity appeared stronger in this case, than either of the former.

Lastly, Mr. Knight, in about the same time, inverted this last direction of the poles, keeping it still parallel to the axis of the cylinder, but causing the smooth end of the stone to attract the north end of the magnetic needle, and the rough end to attract the sonth, and repel the north end of the same needle,

After this report, Mr. Knight proceeded to show, at the meeting, some of the same artificial magnets there mentioned ; and it was found, that the compound magnet, consisting of twelve steel bars, and which had, in the experiment made before the president,

lifted 23 lb. 2} oz. Troy weight, did here, under all the inconve. niencies and disadvantages of a crouded room, still lift a weight amounting to 21 lb. 11 oz.

It was also found, that the single armed block of steel, which had before lifted 14 lb. 2 oz. did here, under the same disadvan. tages as the former, lift 13 lb. 7 oz.

And lastly, Mr. Knight produced to the company the above. mrntioned natural loadstone belonging to Mr. Hauksbee, but with the direction of its polarity again altered from what it was, when it was last seen by the president.

P. S. Since the artificial magnets mentioned in the foregoing paper, Mr. Knight has caused some others to be made of a less size, but of a very great lifting power: and one of these, weighing, without its armour, just an ounce, and with the armour, cramps, and rings, 1 oz. 17 dwt. lifted 6 lb. 10 oz.

This magnet consisted of three plates of steel, each two inches Jong, 7-10ths of an inch in breadth, and not above 6.100ths of an inch in thickness: they were laid flat on each other, and screwed together by two small brass screws going through the three plates. After which, the little parallelopiped block so made up, was armed with iron at the two ends, cramped together with silver, and fitted with a double ring of the same metal, for the convenient holding of it.

[Phil. Trans 1744.

3. By Mr. Benjamin Wilson.

Containing an account of Dr. Knight's method of making artificial Loadstones.

The method was this: having provided himself with a large quan. tity of clean filings of iron, Dr. K. put them into a large tub that was more than one-third filled with clean water; he then, with great labour, worked the tub to and fro for many hours together, that the friction between the grains of iron by this treatment might break off such smaller parts as would remain suspended in the water for some time : the obtaining of which very small particles in sufficient quantity seemed to him to be one of the principal desi. derata in the experiment. The water being by this treatment ren. dered very muddy, he poured it into a clean carthen vessel, leaving the filings behind ; and when the water had stood long enough to become clear, he poured it out carefully, without disturbing such of the iron sediment as still remained, which now appeared reduced almost to impalpable powder. This powder was afterwards removed into another vessel, in order to dry it; but as he had not obtained a proper quantity of it by this first step, he was obliged to repeat the process many times.

Having at last procured enough of this very fine powder, the next thing to be done was to make a paste of it, and that with some vehicle which would contain a considerable quantity of the phlogistic principle ; for this purpose he had recourse to linseed oil in preference to all other fluids With these two ingredients only, he made a stiff paste, taking a particular care to knead it well before he moulded it into convenient shapes. Sometimes, while the paste continued in its soft state, he would put the impression of a seal on the several pieces; one of which is in the British Museum. This paste was then put upon wood, and sometimes on tiles, in order to bake or dry it before a moderate fire, at about a foot distance. The doctor found, that a moderate fire was most proper, because a greater degree of heat made the composition frequently crack in many places.

The time required for the baking or drying of this paste was generally five or six hours, before it attained a sufficient degree of hardness. When that was done, and the several baked pieces were become cold, he gave them their magnetic virtue in any direc. tion he pleased, by placing them between the extreme ends of bis large magazine of artificial magnets for a few seconds or more, as he saw occasion. By this method the virtue they acquired was such, that when any one of those pieces was held between two of his best ten guinea bars, with its poles purposely inverted, it im. mediately of itself turned about to recover its natural direction, which the force of those very powerful bars was not sufficient to counteract.

[Phil. Trans. 1779.

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