began and ended with a strong agitation of the right hand. He frequently uttered dreadful execrations during the fits. The whole duration of his diforder was eighteen years.

At length, viz. in June 1788, he declared that he was poffeffed by feven devils, and could only be freed by the prayers (in faith) of feven clergymen. Accordingly the requifite force was fummoned, and the patient fung, fwore, laughed, and barked, and treated the company with a ludicrous parody on the Te Deum. Thefe aftonishing fymptoms refifted both hymns and prayers, till a fmall, faint voice admonished the minifters to adjure. The fpirits, after fome murmuring, yielded to the adjuration, and the happy patient returned thanks for his wonderful cure. It is remarkable, that during this folemn mockery, the fiend fwore by his infernal den," that he would not quit his patient; an oath, I believe, no where to be found but in the Pilgrim's Progrefs, from which Lukins probably got it.

66

Very foon after the firft relation of this story was published, a perfon, well acquainted with Lukins, took the trouble of undeceiving the public with regard to his pretended disorder, in a plain, fenfible narrative of his conduct. He afferts that Lukins's firft feizure was nothing elfe than a fit of drunkennefs; that he always foretold his fits, and remained fenfible during their continuance; that he' frequently faw Lukins in his fits, in every one of which, "except in finging, he performed not more than most "active young people can eafily do;" that he was detected in an imposture with respect to the clenching of his hands; that after money had been collected for him, he got very fuddenly well; that he never had any fits while he was in St. George's Hofpital, in London; nor when visitors were excluded from his lodgings, by defire of the author of the Narrative; and that he was particularly careful never to hurt himself by his exertions during the paroxyfm.

Is it for the credit of this philofophical age, that fo bungling an impofture fhould deceive feven clergymen

into a public act of exorcifm? This would not have paffed even on the authors of the Malleus Maleficarum, for they required figns of fupernatural agency, fuch as the fufpenfion of the poffeffed in the air, without any vifible fupport, or the use of different languages, unknown to the demoniac in his natural state.

Manferunt, hodieque manent veftigia ruris.

LETTER ON ATTRACTION and REPULSION; communicated by Dr. PERCIVAL, October 11, 1786.

DEAR SIR,

SHALL think myself honoured by your

I communication of the following experi

ments and obfervations to the Manchester Literary Society, if you think them worth their

attention.

THE waving motion of oil and water contained in a glass fufpended and vibrated in ftrings, may be accounted for without confidering any repulfion or difference of gravity between the two fluids. To prove whether a greater difference of fpecific weight would increase the motion, I tried quickfilver and water, and found that in this cafe no waving motion was perceptible. I then tried milk and water,

whofe

whose weights are nearly alike; alfo water tinged with cochineal at the bottom, and clear water above; and obferved that the motion in these was at leaft as great as that of the oil and water. This led me to fufpect that water alone would move in the fame manner, and to make the motion perceptible, I dropped into the glass some powdered yellow ochre during its vibration, which following the agitation of the water, rendered it plainly visible. The glass was then tied to a flip of wood, by which means I could move it with greater velocity in the fame arc: this caufed the waving motion to be fo ftrong as to make the water roll higher on one fide of the furface than the other. Laftly, a cylinder of wood was fufpended by its axis in a bent wire, and the vibration caufed a motion fimilar to that of the fluids.

From these experiments, I conclude that the waving motion is produced by the difference of velocity of the lower and higher parts of the fluid, the higher endeavouring to return fooner than the lower. The higher part of the fluid may be confidered as the ball of a fhorter pendulum than the lower, and the fluidity of the water, or oil, enables its several parts to move as freely as the cylinder of wood which rolls upon its axis, because the center of gravity and of ofcillation do not coincide. The principle is thus explained in Enfield's Inftitutes of Natural Philofophy;

13

"Philofophy; it is eafy to conceive that in a pen"dulum there must be fome one point, on each "fide of which, the momenta of the feveral parts "of the pendulum will be equal, or in which "the whole gravity might be collected without altering the time of its vibrations. This

point, which is called the center of ofcil"lation, is different from the center of gra"vity: for if a plane, perpendicular to the ftring "of the pendulum, be conceived to pass through "the center of the ball, bifecting it, the velo

city of the lower half, and confequently its "momentum, will in vibration be greater than "that of the upper half: confequently, the cen"ter of ofcillation must be lower than the center "of gravity; and a plane paffing through the "center of ofcillation will divide the ball into "two unequal parts, fo that the greater quan

tity of matter above it fhall compensate for "the greater velocity below it, and the mo❝menta on each fide be equal. If the pen"dulum be an inflexible rod, every where of

equal fize, it is found that the diftance of "the center of ofcillation from the point of fufpenfion is two thirds of the length of the "rod. If, whilft a pendulum is in motion, it "meets with an obstacle at its center of ofcilla"tion fufficient to ftop it, the whole motion "of the pendulum will ceafe at once without "any jarring for the obftacle refifts equal

"momenta

" momenta above and below this point." Now gravitation, which is the obftacle to the abovementioned vibrating cylinder, acts upon its axis; and because the lower half has more volocity which is not counterbalanced by quantity of matter above, a waving motion is produced. The reafon that the upper furface remains parallel to the top of the glafs is, because a body revolving about a center has a tendency to recede from that center, fo that a glass may be revolved in a plane perpendicular to the horizon without lofing any of the water. And unless the waving motion when the glafs is vibrated be very violent, it cannot overcome the difference of fpecific weight fo as to caufe an undulation of the upper furface, as appears by the experiment of quickfilver and water, where the weight of the quickfilver, compared with water, renders its waving motion on the furface as imperceptible as that of the water or oil, having air only in the upper part of the glass.

Drops of water rolling over the leaves of colewort are prevented from adhering to the furface by a blue powder, which covers the leaves of that and various other plants, for if the powder be wiped off the water will adhere. The leaves of honey-fuckles and barbery trees are blue on one fide only, and the water adheres to the green fide and not to the blue. If the fur