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injurious effects they might experience from the severity and the variations of the weather.

Lately, however, I have been tempted to ascribe it to the all-powerful effects of caloric. It is well known that cold, where it is not sufficient to condense, diminishes the fluidity of liquids in a greater or lesser proportion, according to the degree of cold required to condense the different fluids; in the same manner, from there being a greater quantity of juices [some of the component parts of the sap may be different in deciduous and evergreen trees-experiments might decide] from the larger size of the vessels through which they pafs, and from the thickness of the leaves and strength of the cuticle being greater in evergreens than in deciduous trees, the former follow the great law which nature has laid down only so far as being thickened, but not sufficiently to stop the circulation entirely, which therefore continues slowly through the colder months of the year, and thereby the leaves are preserved through the winter. In frosty or very cold weather we may observe that evergreens look drooping, which I suppose may arise from the cold being in too large a proportion for the quantity of caloric contained in the tree; evergreens are indeed sometimes killed by severe weather.

Perhaps trees may be hurt by the March winds, from too great an expension of caloric being occasioned by them, and a sufficient quantity not being left to support the health and vigour of the leaves. The caloric which is expired by evergreens may in some measure ameliorate the harshness of the air, and

sometimes felt the want of engravings for the illus tration of particular subjects, I am now perfectly convinced that they would have been given if pofsible. Accept, sir, the sincere good wishes of one who, although an entire stranger to you personally, is an admirer of your abilities, and of the manner in which they are exercised; and begs leave to subscribe himself, with great respect and esteem, your most humble servant, S. H.

P. S. I beg leave to mention, for the consideration of your correspondent Entomophilus, a letter which appeared in "The Monthly Magazine" for August last, stating an instance of a person suffering extremely from an earwig penetrating into his ear; and which, if true, so plainly contradicts the afsertion, in your correspondent's account, of the harmlessnefs of that insect.

To the Editor of Recreations in Agriculture, &c.

SIR,

May 19, 1800.

I SEND you my ideas on the cause of the difference between evergreen and deciduous trees, in hopes that, though not conclusive in themselves, they might however give rise to some more so in the minds of others, if they should be thought worth insertion.

The original and principal cause of the difference between evergreens and deciduous trees has by some been attributed to oxygen, and others to a peculiar kind of varnish, which preserves the leaves from the

injurious effects they might experience from the severity and the variations of the weather.

Lately, however, I have been tempted to ascribe it to the all-powerful effects of caloric. It is well known that cold, where it is not sufficient to condense, diminishes the fluidity of liquids in a greater or lesser proportion, according to the degree of cold required to condense the different fluids; in the same manner, from there being a greater quantity of juices [some of the component parts of the sap may be different in deciduous and evergreen trees-experiments might decide] from the larger size of the vessels through which they pafs, and from the thickness of the leaves and strength of the cuticle being greater in evergreens than in deciduous trees, the former follow the great law which nature has laid down only so far as being thickened, but not sufficiently to stop the circulation entirely, which therefore continues slowly through the colder months of the year, and thereby the leaves are preserved through the winter. In frosty or very cold weather we may observe that evergreens look drooping, which I suppose may arise from the cold being in too large a proportion for the quantity of caloric contained in the tree; evergreens are indeed sometimes killed by severe weather.

Perhaps trees may be hurt by the March winds, from too great an expension of caloric being occasioned by them, and a sufficient quantity not being left to support the health and vigour of the leaves. The caloric which is expired by evergreens may in some measure ameliorate the harshness of the air, and

ence. This latter idea was suggested by the observation, that in colder climates, where there is scarcely verdure, and no inhabitants, so there e no trees to lend their afsistance towards softening the atmosphere. Evergreens appear in a peculiar degree to be natives of northern [polar] climates, as I rather imagine them to be importations from countries where the winters are still more severe than in England.

I should be happy to have my sentiments on this subject either elucidated or rectified, and I remain, in the hope of farther information, your admirer and constant reader, B. C.

As the Editor has at all times a pleasure in obliging those who show an inclination to engage in useful researches, the above has been inserted, though to some it may appear objectionable, on account of the loose manner in which it is written, and the total want of facts to support the hypothesis; but the shortnefs of it may be pleaded in excuse for its insertion.

The writer seems to have forgotten that this miscellany is not calculated for readers in general who are far advanced in the technical knowledge of physics. It is chiefly meant to give general notions on subjects of this nature when they occur, to such as have not previously entered deeply into these researches: of course, it will be expected that when terms purely technical occur, such as oxygen, caloric, &c. that somewhat like a popular explanation of what is meant by these terms should be given, otherwise they can convey no sort of ideas to such readers. Indeed, I am of opinion that it would be an excellent praxis for

young writers when they employ such terms, always to accustom themselves to think what answer they would be able to give to a person of sound understanding, though not technically learned, should he bluntly ask the precise idea annexed to such terms. I am induced to think thus, from having observed the happy effects of a practice of this sort, in regard to common words, that was introduced by a friend of mine in educating a young family, who made it a practice to desire his children to define with some degree of precision such words as they employed, which he selected for that purpose; the consequence of this was, that, although at the beginning they found great difficulty in giving the precise idea conveyed by any word; yet in consequence of the deficiencies of such definitions being pointed out, and the corrections suggested by each other, they came at length to have a much more comprehensive idea of the beauties and defects of language, and exprefsed themselves with more neatness and precision than ever they could have otherwise done. Such of my young readers as shall try this among themselves will be astonished at the vague ideas they have annexed to many words, and the inaccurate manner in which they are accustomed to employ them: nor am I free from suspicion, that were our chemical philosophers thus to tie themselves down to the invariable practice of never using such words as oxygen, hydrogen, nitrogen, caloric, azote, &c. unless when they respectively served to denote a clear idea that they could accurately explain if required, these words would be used more sparingly than they now are. I say no more on that head at present.

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