therefore, should be of such a focus as to allow of its being above the reach of the vapours that arise, and that would

otherwise condense on it and obstruct the view. Some little tact and experience also are required to manage the wires of the battery, because under the compound microscope they appear reversed. I will give an instance or two. When the copper wires were put into a drop of ammonia, a very beauti ful greenish foliated or dendritic structure started from the positive pole, and rushed towards the other. On withdrawing the wires a little from each other, a new growth arose out of the extremity of the previous formation, and generally on coming within a certain distance of the negative pole it assumed the metallic lustre.

Galvanic action has been long known to coagulate albumen: on examining this action under the microscope this thicker or white portion showed itself to be a vesicular struc ture which shrunk up in folds separated in several directions by stronger integuments; while the thin liquid which previously filled them, and gave them in a state of distension complete transparency, spread over the glass dividing and drying in compartments like those of a dragon-fly's wing.

These statements will be ample to put any one in possession of the mode for making similar observations. Further illustrations are unnecessary. The object of this notice is merely to describe a simple arrangement for approaching more nearly the phænomena of chemical action. The microscope will thus open to the chemist new and interminable fields of fascinating inquiry, which cannot but have their use; for although in this mode of operating the several substances must meet each other in unweighed and indefinite propor tions, yet the plan seems to hold out some advantages, at least to facilitate the incipient processes of analysis, and to serve as a guide to subsequent experiments of a more measured kind and on a larger scale. If the observation of re sults is recorded and classified, they must at last lead the practised observer to more than conjectural conclusions as to what he sees; the visible effects under the action of certain agents will become daily more accurately known, till at length the microscopic examination of any substance will go very far to establish its real character.

N.B. Since this paper was read its author has applied a micrometer to the microscope for measuring the angles of the minutest crystals that appear on the field. A short notice of this appeared in Jameson's Journal.

IV. Notice of the Harvest-Bug. By A CORRESPONDENT.

IF

Acarus autumnalis, Shaw.

Acarus Ricinus, Latreille.

F powers of annoyance form a claim to attention, there is none superior to that possessed by the minute insect known in England as the Harvest-bug, and on the Continent, where, according to Latreille's personal experience, its effects are equally serious, as la Louvette.

No good description of it is however extant, and the engraving in Shaw's work bears a very slight resemblance to nature, owing doubtless to the extreme difficulty of obtaining specimens of an insect so nearly invisible to the naked eye. Having been so fortunate as to procure several uninjured harvest-bugs, and having submitted them to a highly powerful magnifier, so as to make a drawing, which underwent many comparisons with the living subject, and is as correct as it is possible to render it, an engraving from it is annexed, for the examination of the curious, together with such particulars as differ from the account of established authorities;-not from any wish to cavil or find fault with those who

to mola

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have done so much for entomology, but with an anxiety, laudable it is hoped, to add (without punning) a mite. to

truth.

The Acarus in question then is a hexapod, of a brilliant scarlet colour: its motion is very swift, and the only way in which the observer can satisfactorily contemplate it is by immersing the insect in a drop of water, in which it swims vigorouslyt, and from which it cannot escape.

The body is oval, sprinkled with stiff hairs, and sixteen very strong ones fringe the hinder part; the legs are horny, like those of a beetle: each foot is furnished with two, and some

• Communicated by Thomas John Hussey, D.D., Rector of Hayes, Kent. + One specimen was still swimming after a lapse of seven hours.

times three, strong claws, with which it works so rapidly, mole-fashion, that it inserts itself beneath the skin in a few seconds. Shaw states that it "adheres to the skin by means of two strong hooks attached to the fore part of the body," but these I have never been able to see: he appears not to have been aware of its burying itself beneath the surface, in which case it is no longer possible to extract it; a small tumour then forms, the itching of which is intolerable. Patience, the panacea universally recommended, is as universally neglected. Serious consequences often arise in an irritable constitution, from broken sleep, and the skin being torn in frantic endeavours to procure relief. External applications are of little avail, the creature being safe beneath the skin; sal volatile, seldom had recourse to till the nails have failed, will change the itching to a pungent smart. As however is the case with all similar scourges, there are individuals perfectly exempt from its attacks.

Shaw, Latreille, and White of Selborne all state that this insect is located upon corn, kidney-beans, and various other vegetables; this they probably adopted from each other, the original foundation being popular belief: but having been assured in the course of my researches on this subject that* Daddy Long-legs (Phalangium Opilio) was the father of Harvest-bugs, and the common red garden spider their prolific mother, and having heard a regular war determined against them as the origin of all the suffering, I may be excused for doubting the value of popular opinions; and let us hope that these absurd fancies of persons who ought to have known better will vanish before the light shed by the popular study of entomology.

The evidence then appears strongly to favour the opinion that the habitat of the harvest-bug is upon, or close to, the ground. White says that " upon the chalk-downs the warrener's nets are sometimes coloured red by them;" and incredible as this may appear to one engaged in contemplating a single specimen, there is no doubt of the truth of the statement, even though it had rested on meaner authority, for the hem of many a Hampshire petticoat has been similarly discoloured, the wearer of which by throwing it off in time prevented the ravages of the insect being extended to the upper part of the person. Experienced sportsmen well know that

Probably from his being frequently covered with another parasitic Acarus, Acarus ocypete.

+Chalk is the favourite soil; and perhaps their abounding in corn-fields is owing to the earth being so dry among the ripe straw, and so warm also.

on the moors they escape the enemy by wearing a close boot. After walking some time upon gravel, far removed from any plant whatever, the stocking will be found sprinkled with them, when, running rapidly upwards, they ensconce themselves wherever the dress is most closely confined to the body. Animals, particularly horses, suffer dreadfully from this cause, the tender skin of the lips and nose being frequently covered with nests of harvest-bugs, which have fixed there during grazing, but which probably cannot bury themselves as in the human being from the toughness of the skin. The cat's whiskers have a scarlet spot at the insertion of each hair*, and she bites her paws all day, yet does not relinquish her favourite bask on the warm gravel, which probably is the cause of her annoyance, because the rabbits, shut up in a building, though fed even on the freshest of kidney-bean plants, are not aware that harvest-bugs exist.

If it be asked where was the embryo harvest-bug,—where was the insect whose life, beginning as it would seem with the greatest heat of summer, ended with the first cold of autumn,during the intermediate nine months? we may reply, Probably buried in embryo in the soil. But research would afford no information on this subject, from the minuteness of the insect. Rectory, Hayes, Kent, March 1836. A. M. H.

V. On the Divergence of Plants, and its Analogy to the Irritability of Animals. By HENRY JOHNSON, M.D.

To the Editors of the Philosophical Magazine and Journal. GENTLEMEN,

IN

N No. 33+ of your valuable Journal you have done me the favour to insert a short communication on the subject of a newly discovered property in plants supposed to be analogous to animal irritability, and which communication has been honoured by the notice of two "friends," whose inquiries and remarks are appended to my paper.

I take great shame to myself for having allowed a whole year to elapse without any attention having been paid, or at least any answer returned, to these very valuable and obliging notices, for which, whilst I apologise for my apparent neglect of them, allow me to offer through you my best thanks to your ingenious and able correspondents.

They probably do not breed in the animal skin any more than in that of their superior prey, because though visible in large groups, each individual seems equally mature.

+ Lond. & Edinb. Phil. Mag., March 1835, vol. vi. p. 164, Third Series. Vol. 9. No. 51. July 1836.

D

At the foot of page 166, your botanical friend asks me if I have ever tried the effect of division on Dirca palustris, or on any plant of the natural order Thymeleæ.

The Dirca palustris is an exotic, and, I believe, a rare plant, which never having seen, I have of course not had an opportunity of making it the subject of experiment.

Belonging to the natural order Thymelea there is one genus only found in England *, the genus Daphne, and of this I have, during the present month, had an opportunity of examining two species, the Daphne Mezereum and Daph. Laureola. On dividing the recent green shoot of this year I found it in both decidedly divergent. They form, therefore, no exception to anything which I have stated in my paper.

At page 169, your medical friend remarks, that the phanomena described in my paper most closely resemble the contraction of the ligamentum nucha by which the head of animals is retracted after death, and which Bichât attributes to vital contractility.

Not having, at present, access to the works of Bichât, I am unable to learn the evidence on which he grounds this opinion. Whether true or not, however, I do not see that it affords an objection to anything which I have advanced.

If this contraction of the ligamentum nuchæ be an instance of vital contractility, and susceptible of excitation by stimuli, it would appear to me to be identical with the irritability or contractility of muscular parts, and analogous to divergence: and therefore not a " distinct property."

If stimulants do not excite contraction in the ligamentum nuchæ, the property, whether vital or not, on which its motions depend, differs in this essential particular from divergence. I am, Gentlemen, yours, &c.

Shrewsbury, May 28, 1836.

HENRY JOHNSON, M.D.

VI. On the Theory of Vanishing Fractions, in Reply to Professor Young. By Mr. W. S. B. WOOLHOUSE.†

WHEN Professor Young's first letter on the theory of

vanishing fractions made its appearance in the April Number of the Philosophical Magazine, the anomalous objections that were urged against my general principles with such apparent confidence were accounted for in my mind by the belief that he had been carried away by a partial and very imperfect perusal of the contents of my essay. Professor * Gray's Natural Arrangement of British Plants. + Communicated by the Author.