A, side view of the last joint of the leg of the blue-bottle fly (musca vomitoria.) three such combs on each foot. It may be remarked, that the insects in question are pretty thickly covered with hair, and the serratures of the combs are employed to free these from entanglement and from dust. Even the hairs on the legs themselves are used in a similar way; for it may be remarked, that flies not only brush with the extremities of their feet, where the curious currycombs are situated, but frequently employ a great portion of their legs in the same way, particularly for brushing one another. Birds are peculiarly distinguished for their cleanliness, which appears to be instinctive; that is, it becomes apparent very soon after they are hatched, at least in those nestlings which are at first blind; the others (Gallina, &c.) do not so much requireit, from their running off immediately out of the nest after their dam. The parents of blind nestlings are particularly careful in watching, after feeding, till they moot, carrying it off in their beaks, an office which they even perform for the female while she is hatching. I have particularly remarked this in the common starling (Sturnus vulgaris), a thing the more necessary, from the bird nestling in the holes 6 of trees; and Colonel Montague observed it in the gold-crested wren (Regulus cristatus, RAY,) in the instance of a nest of young which were fed by the parents after being carried into a room*. In birds,' says White, there seems to be a particular provision, that the moot of the nestlings is enveloped in a tough kind of jelly, and therefore is the easier conveyed off without soiling or daubing. Yet, as Nature is cleanly in all her ways, the young perform this office for themselves in a little time, by thrusting their tails out at the aperture of their nests +. Another delightful writer says, birds are unceasingly attentive to neatness and lustration of their plumage. Some birds roll themselves in dust, and occasionally particular beasts cover themselves with mire; but this is not from any liking or inclination for such things, but to free themselves from annoyances, or to prevent the bites of insects.' I may be permitted to illustrate one of these remarks of Mr. Knapp, by mentioning the fact, that in some parts of Africa the elephant and the rhinoceros, in order to protect themselves from flies, roll themselves in mud, for the purpose of forming an impenetrable crust upon their skin when it becomes dry. Their most formidable insect pest, according to Bruce, is a fly called Isaltaya, belonging, it would appear from the description, to Clairville's Haustellata. It is said not to be larger than a common bee, but is more terrible to those two animals than the lion himself. It has no sting, but insinuates its sucker (haustellum) through the thickest skin, in the same manner as our cleg (Hæmatopota pluvialis, MEIGEN) does. The effects of this sucking are such, that the part not only blisters, but frequently mortifies, and in the end destroys the animal; but the coating of dried mud over the skin affords them effectual protection, and therefore cannot be justly quoted as an instance of their dirty habits. It is highly probable, as it appears to me, that the proverbially unclean habits of swine may be referred to a similar origin, particularly as no animal is more careful to have its bed clean and dry. There is another family of animals no less repulsive to the feelings of many people, though not proverbially dirty as the Nat. Hist. of Selborne, i.269. KNAPP, Journ. of a Naturalist, 311. *Ornith. Dict. Introd. swine, which I have discovered to be peculiarly cleanly; I refer to the several species of spiders. During the course of a series of observations and experiments on the process by which they can shoot lines of their gossamer silk across a brook, or other intervening obstacle, it was indispensable that I should pry with minute attention to their every movement; and I was soon struck with one which interested me not a little, in the instance of one of the long bodied species, (Tetragnatha extensa, LATREILLE.) It appeared to be mumbling, if I may use the term, its legs between its mandibles, drawing each leisurely along, as a dog may be seen to gnaw a bone when not very much in earnest, but more by way of pastime than of making a dinner. I could not at first account for this; the ancient naturalists, who drew largely on their imagination when facts failed them, would at once, I have no doubt, have leapt to the conclusion, that the spider, in default of prey, actually devoured its own legs, as it has been asserted to do its web*. A little attention convinced me, that the movements alluded to were precisely of the same kind as the preening of birds. Spiders have their legs more or less covered with sparse hair, which, being rather long and bristly, is apt to catch up bits of their own web and other extraneous matters, and these, from the delicacy of their semi-transparent skin, must produce uncomfortable irritation. To free themselves from this is one of their daily occupations; and when a spider appears to the less minute observer to be quite at rest, it will often be seen, on close inspection, to be assiduously and slowly combing its legs in the manner I have above mentioned. The term combing is very appropriate in the instance of the common garden-spider (Epeira diadema), which is furnished with a set of teeth somewhat in form of a comb; but it has another instrument in addition to this, peculiarly useful in the process, consisting of a smooth and somewhat curved horny needle, which bends over the teeth of the comb, and holds the limb which it is dressing more firmly down, as if, after entering it in the hair, we were to apply a finger over the edge of one of our artificial combs. In some other spiders (Dysdera erythrina, &c.), there is, in the situation of the comb just described, a closely set brush of * BLOOMFIELD's Remains, vol. ii. thick hairs, which is employed in the same way. Any person who will take the trouble may readily verify these observations by confining a spider in a wine-glass, placed in a saucer filled with water, from which it cannot escape, so long as there is no current of air to carry off a silken line for a bridge. Those who have paid attention to ants, may have remarked that a pair of them may be often seen touching one another with their antennæ, and even passing their tongues over part of each other's bodies, in the same way as they are seen to do with their eggs, larvæ, and pupæ, erroneously imagined by the ancients to be hoarded grain. The necessity which they are under of moving these to various parts of the colony, in consequence of variations in the weather, must often expose them (polished though they be) to soiling; but the careful nurses instantly remove every thing of this sort with their mandibles, or tongue -movements which have been misinterpreted, as licking the pupæ into shape; as the bear is no less erroneously asserted to do by her cubs. In all such cases, cleanliness seems to be the chief, if not the sole, motive; as those mutual caresses of the working ants are, I think, for the same purpose. These, indeed, remind me strongly of the common practice of horses and cows of cleaning each other's necks and heads, which the individual cannot itself reach with its tongue; and, in the same way, caged birds will sometimes do the friendly office to a fellow-prisoner, of pecking off anything extraneous adhering to the head or the bill, where preening is impossible, and the foot is seldom well adapted to the purpose. Such are a few of the illustrations which have suggested themselves to me upon this subject: should they be found interesting, I may probably add a few more at a future opportunity. Lee, Kent, 1st July, 1830. Ν DESCRIPTION AND APPLICATION OF A TORSION GALVANOMETER. BY WILLIAM RITCHIE, A.M., F.R.S. Assoc. Mem. S. A. for Scotland, Rector of the Royal Academy of Tain. IN a paper which appeared in the first part of the Philosophical Transactions for 1830, I investigated the elasticity of threads of glass, and applied that property to the construction of a delicate and accurate galvanometer. The instrument then described, though sufficient for most purposes, requires some modification to adapt it to researches of extreme delicacy. The description of the instrument, in this more perfect state, with a few of its numerous applications, will form the subject of this communication. For experimental researches in electro-magnetism, it is extremely useful to have constantly at hand a quantity of copper wire, of different degrees of fineness, coated with sealing-wax. The most convenient mode of giving the wire this coating, is the following:-Stretch the wire between two supports, heat it gradually, from one end to the other, with an iron bar, or spirit-lamp, and continue rubbing the heated part with a stick of sealing-wax; the wire will receive a fine coating, sufficient to prevent metallic contact when portions of it are pressed together in the construction of any piece of electro-magnetic apparatus. Take the wire thus coated, heat it slightly to prevent the wax cracking, and form it into a rectangular shape, consisting of six, eight, or ten repetitions of the wire, according to the delicacy of the instrument required. The upper side of the rectangle must then have the wires separated into two equal portions, bent round a small cylinder, and then continued straight, so as to leave a circular opening in the middle, about one-third of an inch in diameter. The use of the circular opening, in the upper side, is to allow a slender axis, carrying the magnetic needles, to pass through it, in order to increase the power of the instrument, and render the compound needle |