was that day almost covered with water. After this, it continued to thaw every day about noon when the sun was out; and by the 23d of April the ground was in many places bare. On the 26th it rained very fast, almost the whole night, which was the first rain after October the 3d, 1768.

During most of the winter months, November, December, January, February, and March, the thermometer without was considerably below zero, the lowest of all being — 45, that is, 45 below 0, which was on the 22d of January. And the highest state was + 80, viz. on the 3d of July.

Observations on the Aphides of Linnæus. By Dr. WILLIAM RICHARDSON, of Ripon, Yorkshire. —[1771.]

Where

THOUGH the aphides are distinguished by Linnæus into more than 30 species, still Dr. R. is satisfied, from his own observation, that the distinct species are even double that number: nor can he altogether agree with this ingenious author, that there are a greater variety of plants producing aphides than there are different sorts of this insect. plants are of a like nature, they are usually frequented by the same insects; but many of these plants will be found to support two or more quite different sorts. On the peach and nectarine, indeed, the aphides are the same, and he did not find on these trees more than one sort. The plum-tree, on the other hand, has two sorts, very distinct from each other; one of a yellowish green, with a round short body; the other of a bluish green, as it were enamelled with white, and the shape more oblong. On the gooseberry-bush and currant the same aphides may be found; but each of these is inhabited by two very different species; one being of a dusky green, with a short plump body; the other of a paler green, the body more taper, and transversely wrinkled. To these instances he further adds, that the rose-tree supports not less than three distinct species; the largest of which is of a deep green, having long legs of a brownish cast, with the joints of a very dark brown, as are also the horns and antennæ; a second sort is paler green, has much shorter legs, and a more flat body; the third sort is of a pale red, its body transversely wrinkled, and is most frequently on the sweetbriar.

If, at the beginning of February, the weather happens to be so warm, as to make the buds of the rose-tree swell and appear green, small aphides are frequently to be found upon them, not larger than the young ones in summer, when first

U

produced. But there being no old ones to be found at this time of the year, which in summer he had observed to be viviparous, he was formerly not a little perplexed by such different appearances, and was almost induced to give credit to the old doctrine of equivocal generation.

Those which withstand the severity of the weather seldom come to their full growth before the month of April; at which time they usually begin to breed, after twice casting off their exuviæ, or outer covering. It then appears that that they are all females, which produce each of them a very numerous progeny. As before observed, they are viviparous; and what is equally uncommon, the young ones all come into the world backwards. When they first come from the parent, they are enveloped by a thin membrane, having in this situation the appearance of an oval egg; which probably induced Reaumur to suspect that the eggs discovered by Bonnet were nothing more than abortions. This egg-like appearance adheres by one extremity to the mother, while the young one contained extends the other; by that means gradually drawing the ruptured membrane, over the head and body, to the hind feet. During this operation, and for some time after, by means of something glutinous, the fore part of the head adheres to the vent of the parent. Being thus suspended in the air, it soon frees itself from the membrane in which it was confined, and after its limbs are a little strengthened, is set down on some tender shoot, and then left to provide for itself. When the spring proves mild, and consequently favourable to this kind of insect, Dr. R. has observed not only the rose-trees, but various kinds of fruittrees, to be greatly injured by them.

In the spring months, there appear on the rose-tree only two generations of aphides, including those which immediately proceed from the last year's eggs: the warmth of the summer adds so much to their fertility, that no less than five generations succeed each other during that interval. One is produced in May, which twice casts off its covering; while the months of June and July each supply two more, which cast off their coverings three or four times, according to the different warmth of the season. This frequent change of the outer covering is the more extraordinary, as it is the oftenest repeated when the insects come the soonest to their growth; which Dr. R. has sometimes observed to happen in ten days, where warmth and plenty of nourishment have mutually conspired.

Early in the month of June, some of the third generation,

which were produced about the middle of May, after casting off their last covering, discover four erect wings, much longer than their bodies; and the same is observable in all the succeeding generations, which are produced during the summer months, without, however, distinguishing any diversity of sex, as is usual in several other kinds of insects. For some time before the aphides come to their full growth, it is easy to discover which of them will have wings, by a remarkable fulness in the breast, which in the others is hardly to be distinguished from the body. When the last covering is rejected, the wings, which were before folded up in a very narrow compass, gradually extend themselves in a most surprising manner, till their dimensions are at last very considerable.

A very small black ichneumon fly, with a slender body, and very long antennæ, darts its pointed tail into the bodies of the aphides, at the same time depositing an egg in each. This egg produces a worm, which feeds on the containing insect, till it has acquired its full growth; when it is usually changed to that kind of fly from which it had its origin. In this, however, it is sometimes prevented by another sort of small black fly, which wounds this worm through its pearllike habitation; and by laying one of its eggs in it, instead of the former fly, produces its own likeness.

In the autumn, Dr. R. finds three more generations of aphides to be produced; two of which make their appearance in the month of August, and the third usually before the middle of September. As the first two differ in no respect from those which are met with in summer, it would be wasting time to dwell any longer on them; but the third, differing greatly from all the rest, demands our giving it a more serious attention. Though all the aphides which have hitherto appeared were females, in this tenth generation are found several male insects; not that they are by any means so numerous as the females, being only produced by a small part of the former generation. To which Dr. R. further adds, that he has observed those which produce males previously to have produced a number of females, which in all respects resemble those already described.

The females have at first altogether the same appearance with those of the former generations; but in a few days their colour changes from a green to a yellow, which is gradually converted into an orange-colour, before they come to their full growth. They differ likewise in another respect, at least from those which occur in the summer, that all those yellow

females are without wings. The male insects are, however, still more remarkable, their outward appearance readily distinguishing them from the females, of this and all other generations. When first produced they are not of a green colour, like the rest, but of a reddish brown; and have afterwards, when they begin to thicken about the breast, a dark line along the middle of the back. These male insects come to their full growth in about three weeks' time, and then cast off their last covering; the whole insect being after this operation of a bright yellow, the wings only excepted. But they soon change to a darker yellow, and in a few hours to a very dark brown; if we except the body, which is something lighter coloured, and has a reddish cast. They are all of the winged sort; and the wings, which are white at first, soon become transparent, and at length appear like very fine black

gauze.

Though Dr. R. has observed that the contents of the eggs have the appearance of a uniform fluid; that this cannot in reality be the case, sufficiently appears from the aphides they produce in the spring, without any other aid than the warmth of the season. Nor is a single insect to be esteemed the whole product of an egg, since it has been clearly shown, that ten generations succeed each other; the first rudiments of which must have been originally in the egg. The wonder however becomes still greater, when we consider the number of individuals in each generation; this being, he is fully convinced, at a medium, not less than 50. Whoever pleases to multiply by 50, nine times over, may by this means form some notion of the great number of insects produced from a single egg; but will at the same time find that number so immense, as to exceed all comprehension, and indeed to be little short of infinity.

Astronomical Observations made, by Appointment of the Royal Society, at King George's Island in the South Sea. By Mr. CHARLES GREEN and Lieutenant JAMES COOK.

THE first appearance of Venus on the sun was certainly only the penumbra, and the contact of the limbs did not happen till several seconds after, and then it appeared as in fig. 1. This appearance was observed both by Mr. Green and me; but the time it happened was not noted by either of us: it appeared to be very difficult to judge precisely of the times that the internal contacts of the body of Venus happened, by reason of the darkness of the penumbra at the

sun's limb, it being there nearly, if not quite, as dark as the planet.

At this time a faint light, much weaker than the rest of the penumbra, appeared to converge towards the point of contact, but did not quite reach it: see fig. 2. This was seen by myself and the two other observers, and was of great assistance to us in judging of the time of the internal contacts of the dark body of Venus, with the sun's limb.

2

3

The first internal contact, or the limb of Venus, seemed to coincide with the sun's, as represented by fig. 3.

By

The Quantity of the Sun's Parallax, as deduced from the Observations of the Transit of Venus, June 3. 1769. THOMAS HORNSBY, M.A. F.R. S.-[1771.]

THE uncertainty as to the quantity of the sun's parallax, deduced from the observations of the transit of Venus in 1761, (whether it arose from the unfavourable position of the planet, so that a sufficient difference of time in the total duration of the transit was not, and indeed could not be, obtained from observations made at different places; or from the disagreement of the observations of different astronomers, which were to serve as terms of comparison,) seems now to be. entirely removed; and from the observations made in distant parts by the astronomers of different nations, and especially from those made under the patronage and direction of this society, the learned of the present time may congratulate themselves on obtaining as accurate a determination of the sun's distance as perhaps the nature of the subject will admit. The parallax on the third of June being 8".65, the mean parallax will be found to be = 8".78; and if the semidiameter of the earth be supposed 3985 English miles, the mean distance of the earth from the sun will be 93,726,900 English miles.

C

Observations on Vegetation. By Mr. MUSTEL of Rouen.

MANY celebrated writers, induced by the analogy which they observed between the vegetable and animal kingdoms, have admitted the circulation of the sap in the one, in a similar manner to the circulation of the blood in the other.