benefit of man, he traverses the fandy deferts of Arabia, where drink and pasture are feldom to be found; and will continue fix or feven days without fuftenance, yet ftill patient of labour. His hair is manufuctured into cloathing; his flesh is deemed wholesome nourishment; and the milk of the female is much valued by the Arabs. The camel, therefore, for fuch is the name given to this animal, is more worthy of your admiration than the tiger; notwithstanding the inelegance of his make, and the two bunches upon his back. For mere external beauty is of little estimation; and deformity, when affociated with amiable difpofitions and useful qualities, does not preclude our respect and approbation.

PHILOSOPHICAL ATTENTION AND

A

SAGACITY.

N attentive and inquifitive mind often derives very important instruction from appearances and events, which the generality of mankind regard as trivial and infignificant.

infignificant. Permit me, Alexis, to offer to you a few examples of the truth of this obfervation. You have frequently remarked, and perhaps admired the volubility and luftre of the globules of rain, that lie upon the leaves of colewort, and of other vegetables; but I dare fay, you have never taken the trouble of infpecting them narrowly. Mr. Melville, a young philofopher of uncommon genius, was ftruck with the phænomenon, and applied his attention to the investigation of it. He difcovered that the luftre of the drop is owing to a copious reflection of light, from the flattened part of its furface, contiguous to the plant; and that when the drop rolls over a part, which has been wetted, it instantly loses all its brightness, the green leaf being feen through it. From these two obfervations he concludes, that the drop does not really touch the plant, whilst it retains a mercurial appearance, but is fufpended by the force of a repulfive power. For there could not be any copious reflection of white light, from its under surface, unless there was a real interval between it and the

plant. And if no contact be fuppofed, it is easy to account for the wonderful volubility of the drop, and why no traces of moisture are left wherever it rolls.

From this reafoning we may conclude, that when a polished needle is made to fwim on water, it does not touch the water, but forms around it, by a repulfive power, a bed, whose concavity is much larger than the bulk of the needle. And this affords a much better explanation of the fact, than the common one, deduced from the tenacity of the water. For the needle may be well conceived to fwim upon a fluid lighter than itself, fince the quantity of water thus difplaced, by repulfion, must be equal to the weight of it. And this instance leads us to a juft and neceffary correction of the hydrostatical law, that the whole fswimming body is equal in weight to a quantity of the fluid, whofe bulk is equal to that of the part immerfed. For it should be expreffed, that the weight of the Swimming body is equal to that of the weight of the quantity of fluid difplaced by it.

A very ingenious friend of mine, during his refidence at the university, undertook a course of experiments, to afcertain the heat or cold produced by the folution of certain substances in fpirit of wine. Whenever he withdrew the thermometer from the spirit, and suspended it in the air, he uniformly observed, that the mercury funk two or three degrees, although the spirit of wine, in which the inftrument had been immerfed, was even colder than the furrounding atmosphere. This fact he communicated to the profeffor of chemistry; who immediately suspected, that fluids by evaporation generate cold; an hypothefis, which he afterwards verified by a variety of beautiful, and decifive trials.

When Sir John Pringle and Dr. Franklin were travelling together in Holland, they remarked, that the track-fchuyt, or barge, in one of the ftages, moved flower than usual, and inquired the reason of it. The boatman informed them, that it had been a dry season, and that the water was low in the canal. He was asked, if the

water was fo low that the boat touched the muddy bottom of the canal? to which he anfwered in the negative; adding, however, that the difference in the quantity of water, was fufficient to render the draught more difficult to the horfe. The travellers, at firft, were at a lofs to conceive, how the depth of the water could affect the motion of the boat, provided that it fwam clear of the bottom. But Dr. Franklin, having fatisfied himself of the truth of the boatman's observation, began to confider it attentively; and endeavoured to account for it in the following manner. The barge, in proceeding along the canal, must regularly difplace a body of water, equal in bulk to the space which fhe occupies; and the water fo removed must pass underneath, and on each fide of her. Hence if the passage, under her bottom, be ftraitened by the shallows, more of the water must pass by her fides, and with greater velocity, which will retard her course, because fhe moves the contrary way. The water, also, becoming lower behind than before the boat, she will be preffed back by the weight of its difference