The conjunctions of the Moon with Mercury and Venus on 5th January; with Venus on 5th September; with Mars on 10th August; and with Saturn on 3d July will not be occultations anywhere on the globe.

The method of computing an occultation, given in these collections, No. XX, Art. 3, is the same in principle as Du Séjour's, which is fully detailed and demonstrated in his "Traité Analytique des Mouvemens Apparens des Corps Célestes." It is there shown, (Vol. I. p. 270), that the supposition of the portion of the moon's orbit, described during an eclipse or occultation, being a straight line, causes insensible errors only. An error of greater magnitude may arise from the horary motion being esteemed uniform, while it is generally variable; but this error can be easily corrected by using the horary motion corresponding to the middle of the particular interval under consideration.

In the precepts for computing an observed occultation in the article alluded to, reference is made to the denomination (North or South) of the moon's nearest approach, which is not set down in the elements published in the Nautical Almanac, as it is always the same as that of the difference of declinations at the conjunction.

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ART. XII. ANALYSIS OF SCIENTIFIC BOOKS.

I. Philosophical Transactions of the Royal Society of London, for the year 1825. Part the Second.

In our quarterly reports of the proceedings of the Royal Society, we have given brief and general abstracts of the principal papers contained in the volume before us; a more detailed and accurate abridgement of their contents will form the subject of the following article.

i. On the Anatomy of the Mole-cricket. By J. Kidd, M. D., F. R. S., Regius Professor of Medicine in the University of Oxford.

This singular insect is described under various names; as the earth-crab, from its general appearance; vermis cucurbitarius, from the mischief it does to cucumber-beds. By the French naturalists it is called courtilière.

The best account of it is in a well-known entomological work by Rösel, published at Nuremberg, in 1749. This account is accompanied by the best engravings also of the external characters of the animal in its different states; and the value of these engravings is greatly enhanced by the accuracy with which they are coloured.

Rösel says, that about the month of June or July, rarely later, the gravid female gryllotalpa excavates a cavity, from four to five inches beneath the surface of the earth, in which she deposits her eggs in one heap, to the number of three hundred or more, and dies within a few weeks afterwards. At the end of about a month, the young mole-crickets are produced; and appear, on a hasty survey, to bear a general resemblance to the ant. Between the time of their birth and the commencement of winter, the young animals cast their skin three times; they lie dormant during the winter, deeper in the earth in proportion to the inclemency of the season; and during this period cast their skin for the fourth time. About May they leave their winter-quarters, and at this time are furnished with the rudiments of their future wings, four in number; which differ remarkably in size and form and position from those of the perfect insect, in which the inferior wings are folded in a very curious manner, while in the imperfect insect they are always open.

During the month of June or July they cast their skin for the fifth and last time; after which the wings acquire a perma

nent character, and the insect becomes capable of propagating its species.

It appears from Rösel's account, that while very young, these insects are gregarious, but not afterwards; that they are usually found in the vicinity of meadows and of fields of corn, particularly of barley; to which they are very detrimental by feeding on the roots, and thus intercepting the due nourishment of the plants themselves. Our author has met with the mole cricket in one situation only, namely, in some peat-bogs, at the distance of a few miles to the west of Oxford. In the neighbourhood of these peatbogs the insects are familiarly known by the name of croakers, from the peculiar sound which they occasionally make; a sound not very unlike, but more shrill and more soft than that of the frog. This sound, even in the case of a single individual, may be heard at the distance of some yards; but when made by numerous individuals at the same time, it may be heard at the distance of some hundred yards, provided the air be in a favourable state. The insect is usually found within a foot and a half of the surface, and in parts where the peat is neither quite dry, nor very moist; of such a consistence, indeed, as is most favourable to the mining operations of the animal.

The accounts of different authors differ as to the food of the mole-cricket. Having kept several individuals in glass vessels during some weeks, Dr. Kidd observed, that of all kinds of vegetable food, they preferred the potato, while cucumber they hardly touched; but if raw meat were offered them, they attacked it with great greediness, and in preference to every thing else. And, when they had been kept, even but for a short time, without any food, they did not hesitate to attack each other; in which case the victor soon devoured the flesh and softer parts of the van. quished. As I have not unfrequently found them in their native haunts, maimed in various parts of the body, I have very little doubt that, although captivity may increase their ferocity, they are not, even in a natural state, free from each other's attacks. If they are carnivorous, they probably feed on worms and various larvæ, which are abundant in the peat-bogs above-mentioned, for I have repeatedly found the horny and indigestible parts of insects within their stomachs. Similar relics I have found in the stomach of the pneumora and gryllus viridissimus. The two following facts attest, in the tribe of insects to which the molecricket belongs, a remarkable degree of voracity, and an equally remarkable power of abstaining from food. My friend Dr. Macartney, of Dublin, informs me that he has known a gryllus devour a portion of its own body: on the other hand, my friend Mr. Buckland, of this University, gave me, at the commencement of the present summer, a living gryllotalpa, which had been confined during nine or ten months in a tin case containing a small quan◄

tity of garden mould, without the possibility of having met with any other nourishment than such as that portion of mould might be supposed to contain.'

In the external characters of the perfect gryllotalpa, we see a perfect accommodation in form and structure to the circumstances in which the individual is naturally placed. Destined, like the common mole, to live beneath the surface of the earth, and to excavate a passage for itself through the soil which it inhabits, the gryllotalpa is furnished, like the mole, with limbs particularly calculated for burrowing; with a skin which effectually prevents the adhesion of the moist earth through which it moves; and with exactly that form and structure of body, by which it is enabled to penetrate the opposing medium with the greatest ease. At the same time, in order to prevent the necessity of its excavating a track so wide as to admit of the body being turned round in case of a desire to retreat, it is endued with the power of moving as easily in a retrograde as in a progressive direction; and, apparently to perform the office of antennæ, which warn the insect of approaching danger in its progressive motions, it has two appendages, which might not improperly be called caudal antennæ, evidently calculated to serve a similar purpose during its retrograde motions; particularly as they are furnished with very large The indifference with which the insect is disposed to move in either direction is manifested by the following experiment: if touch it towards the head, it retreats; if towards the other extremity of the body, it advances.

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The general colour of the animal is such as indirectly to serve as a protection to it, being nearly of the same hue as the vegetable mould in which it lives; so that it is not very readily distinguished upon being first turned up to view; and its safety seems to be still farther insured by the appearance of death, which, in common with many other insects, it assumes when suddenly disturbed. This stratagem, for so it may be called, appears to be most decidedly practised by the animal while in captivity; and if thrown at random out of the vessel in which it has been confined, however unnatural the posture may be into which it has been thrown, it remains as it were in a state of catalepsy during half a minute or more; the first indication which it gives of recovery from this stupor, invariably consists in a motion of the extremity of the antenna.

The general colour of the insect is a dusky brown, passing either into a reddish brown, or into an ochery yellow; those parts being of the darkest colour which are most exposed to view when the animal is moving in the open air. Every part of the body is to a greater or less degree covered by a kind of down, which seems to be the efficient cause of its capability of repelling moisture; which capability is so remarkable, that when the insect is