Oldalképek
PDF
ePub

branches of the fame tree that were abroad, the bloffoms were but just beginning to fhew themfelves. In fhort, none of these internal branches appeared to be in the leaft degree affected by the froft-nipt ftate of their trunks; but were as forward, as if the intire trees or fhrubs had been in the hot-house.

The refult will eafily be conjectured of the converse of this experiment. The trees, &c. that were placed in the infide of the hot houfe, had their branches covered with leaves and flowers about the middle of May; while the fingle branch of each that was carried to the outfide, was abfolutely at this time in the very fame state with thofe that grew abroad, exhibiting the fame appearances that trees prefent during the winter, and deriving no advantages from the warm fituation of their refpective trunks and branches within the hot-house.

It seems evidently to follow from thefe experiments, that there is no regular or general circulation of the fap in trees between the trunk and the branches; as thefe laft, which were admitted into the hot-houfe, vegetated vigorously, while their trunks and their other branches were in a ftate of torpidity or inaction, and covered with ice. They likewife prove, that each part of a tree is furnifhed with a quantity of fap, independent of any fupply from the trunk or other branches, fufficient to effect the firft production of buds, flowers, and fruits, provided that these juices are put into motion by heat.

An accident that attended the Author's course of experiments, fuggefts a ufeful improvement in the treatment of fruit trees. A fnail having gnawed and deftroyed the petals, and the famina, or male flowers, of three of the flower buds of one of his apple trees, but without hurting the piftillum, he was furprized to find that they produced fruit, while the greater part of the other flowers, which had not been injured, did not bear Taking a hint from the fnail, the Author cut with his fciffars the petals of different apple, pear, plum, and cherry bloffoms, close to the calyx. Almost every one of the flowers, thus treated, bore fruit; while feveral of the neighbouring flowers mifcarried. It will naturally be fuppofed that the deftruction of the stamina would render the fruit barren, or that it would want thofe feeds that contain the germen that is to perpetuate the species. Accordingly, in cutting open the apples whofe petals and ftamina were eat up by the fnail, he found. the capfule formed as ufual at the center of them; yet they were entirely empty, without the leaft appearance of a pip."

In the 12th Article are contained fome circumftances communicated by Dr. Ducarel, relating to the early cultivation of botany in England; and particularly concerning the celebrated John Tradefcant, a great promoter of that fcience, as well as of natural history, in the last century. In the 22d article is given

a de

a defcription and delineation of a rare American plant of the Brownææ kind,' by M. P. J. Bergius. Article 5th contains the catalogue of 50 plants prefented annually to the Royal Society by the company of Apothecaries.

NATURAL HISTORY.

In the 2d Article, Mr. Adam Walker briefly defcribes the petrefactions and other natural curiofities of the cavern of Dunmore Park, near Kilkenny in Ireland. In the 3d, Dr. Michael Morris gives a fhort account of fome fpecimens of lead ore, containing native lead, found in a mine in Monmouthshire. The 19th Article is a table conftructed by Dr. William Withering, afcertaining the principles of twelve different kinds of marle found in Staffordshire: And in the 21ft Article, the Hon. Daines Barrington describes a foffil lately found near ChristChurch in Hampshire.

PAPERS relating to ELECTRICITY and METEORS.

The 6th Article is a fhort extract of a letter from Mr. Kinnerfley to Dr. Franklin; in which after taking notice of the remarkable conducting quality of fome kinds of charcoal, and observing that a strong line drawn on paper with a black-lead pencil will conduct an electrical fhock pretty readily, he mentions the effects of a late thunder ftorm in Philadelphia. A floop and three houfes were, in less than an hour's time, all ftruck by it. The floop, and two of the houfes, were confiderably damaged; but the third, which was provided with a cylindrical iron conductor, only half an inch thick, confifting of an affemblage of feveral rods strongly screwed together, the least of which was funk 5 or 6 feet under ground, was preferved from all kind of injury, by means of the apparatus; which had evidently fuftained the fhock, and conducted the lightning, with no other injury to itself than the melting of 6 inches and a half of the flendereft part of a brafs wire fixed on the top of it. Captain Falconer was in the houfe during the accident, and obferved the explofion to be an aftonishing loud one.' Article 8. A Report of the Committee appointed by the Royal Society, to confider of a method for fecuring the Powder Magazines at Purfleet.

Article 9. Obfervations upon Lightning, &c. By Benjamin Wilfon, F. R. S. &c.

Article 10. A Letter to Sir John Pringle, Pr. R. S. on pointed Conductors.

We have already given the substance of fome of Mr. Wilfon's objections, offered in the 9th Article, to the report which forms the fubject of the 8th, and to a part of which he had formally expreffed his diffent in writing. [See our Review for laft Month, page 386.] Thefe objections having been maturely confidered by the committee, they, in the 10th article, declare that they

ftill

i

ftill find no reafon to change their opinion, or to vary from their former report in favour of pointed conductors. The fubfcribing members of this committee are the Hon. Mr. Cavendish, Dr. Watson, Dr. Franklin, and Mr. J. Robertson.

Article 20. An Account of a fury Meteor feen on February 10, 1772,' near Berwick; and of fome new electrical Experiments. By Patrick Brydone, Efq;

Whether all the meteors that have been defcribed and recorded in the Philofophical Tranfactions have had any just pretenfions to a place in that refpectable collection, may perhaps be doubted. The prefent, however, feems juftly intitled to that rank, as well on account of its fplendour and duration, as of its height; and ftill more on account of the data from which that height may be estimated. It appeared in the form of a fplendid flame of a conical figure, the light of which almoft extinguished that of the moon, then about half full; moving nearly horizontally through a space of about 30 degrees, at about the height of 50 degrees, and feemed to burft at the end of 10 or 12 feconds into a number of sparks, resembling the ftars in a fky-rocket.

The Author expecting a report, had the prefence of mind to take out his watch, which had a fecond hand; but after stopping above 4 minutes without hearing any, he rode on. In about a minute afterwards, however, he was stunned by a loud and heavy explosion, refembling the discharge of a large mortar at no great diftance, and followed by a kind of rumbling noife like that of thunder.' On examining his watch, he found that the found had taken 5 minutes and about 7 feconds to reach him; which, according to the common computation of 1142 feet in a fecond, gives a diftance of at least 66 miles. At a place diftant about 20 miles Weft, this meteor, the appearance of which was likewife followed by a loud report, was feen by two gentlemen, nearly at the fame height as it was per ceived by Mr. Brydone: fo that its diftance from the earth was probably greater than the fenfible limits of our atmosphere. This phenomenon, we shall observe, as well as many others, furnishes a ftrong prefumption that the air is not the only medium of found as the violent report occafioned by it originated probably in a region, where there was as near an approach to a vacuum as any that we can make with our best air pumps.

In the remaining part of this article, the Author relates fome experiments in which he charged an infulated conductor, by rubbing the back of a cat. The animal, however, not patiently fubmitting to the experiment, the fame effects were produced on a young lady's combing the hair of her fifter's head, which, however, we fhould obferve, had not, like the hair of most other young ladies, been matted together and defiled by a paste of

pomatum

3

pomatum and powder. On caufing the pointed wire of a coated vial to follow the comb, the vial was highly charged, fo as to give a fmart fhock, and fet fire to fpirits.

In these experiments, the Author's difpofition of the two ladies does not appear to us to have been perfectly scientific. The lady who performed the office of the rubber, ought not to have stood on wax; unless indeed to fhew occafionally that fhe likewife became electrified, but with a contrary electricity, on the approach of any body communicating with the earth: and the lady whofe hair was combed fhould have been infulated, in order to produce the greateft effect.

In the 23d Article is given an account of fome of the effects of a thunder ftorm, in which Mr. Heartly was killed in his bed. Mrs. Heartly, who lay on his left hand, was awakened by the explosion, and found her right arm ftunned and benumbed, and a little painful. Not being alarmed, however, fhe fell asleep, and did not difcover, till fhe awoke in the morning, that her husband had been killed by it. Though the bed poft was split into many fhivers, one of which was found within his nightcap, no marks were discovered on any part of his body; except that his right cheek was fwelled, and his hair on that fide confiderably finged, as was the infide of his nightcap on the fame fide, while no fuch marks appeared on its outfide.

The 13th Article contains only fome thermometrical obferva-
tions relating to remarkable degrees of cold obferved on the
Continent in 1767, 1768, and 1770, by M. J. H. Van Swinden.
CHEMISTRY.

Article 16. Actual Fire and Detonation produced by the Contact of
Tinfoil, with the Salt compofed of Copper and the nitrous Acid.
By B. Higgins, M. D.

Before we give the fubftance of this curious experiment, it will be proper to premife a difcovery of the Author's, relating to the metallic falt produced by a combination of the nitrous acid with copper; which he found to poffefs the peculiar property of taking fire, and deflagrating in a degree of heat not greater than can be borne by the hand. This quality is moft conveniently fhewn by twice or thrice dipping a piece of foft bibulous paper into a faturated folution of copper in fpirit of nitre, and alternately drying it with a gentle heat. If the paper, thus copiously impregnated with the cupreous falt, be then held at a moderate diftance from the fire, it will deflagrate and burn to a brown calx.

The fuccefs of the following experiment depends on the ready accenfibility of this metallic falt. A fufficient quantity of it in a fomewhat moift ftate, procured by putting feveral pieces of thin fheet copper into a weakened fpirit of nitre, is to be beaten to the fineness of basket fea falt, and ftrewed to the

thickness

[merged small][ocr errors]

thickness of a fhilling on a piece of tinfoil, twelve inches in length, and three in breadth. The foil is then to be inftantly rolled up, fo as to include the falt, as it lies, between the coils. The ends being pinched together, and the whole pressed flat and clofe, the following phenomena fucceffively prefent themselves. First, a part of the falt deliquefces, and, being impregnated with the tin, a frothing is perceived at the ends of the coil, attended with a moderate warmth, and followed by a copious emiffion of nitrous fumes. The heat then increases so as to become intolerable to the fingers; and, at length, explosion and fire are perceived, which burft and melt the tinfoil, if it be very thin. Those who would repeat the experiment must confult the Author's own account of it, as the fuccess in a great measure depends on an attention to fome minute circumstances which we have not room to mention.

The Author's rationale of this procefs is principally founded on the abovementioned property of the cupreo-nitrous falt, or on its eafy ignition in a flight degree of heat. Its acid is fuppofed in part to quit the copper, and to attack the tin *; in its commenftruation with which metal, a confiderable effervefcence and heat are produced, fufficient to dry the remaining undecompounded cupreous fa't, and to fet it on fire. The ig nition may likewife, we imagine, be in fome meafure the confequence of a nitrous fulphur extemporaneously formed, by the rapid combination of the nitrous acid with the phlogifton of the tin, and which is inftantaneously kindled and diffipated in the very act of its formation.

ANTIQUITIES.

Article 4. Farther Remarks upon a Denarius of the Veturian Family, &c. By the Rev. John Swinton, B. D. F. R. S. &c. In the 58th volume of the Philofophical Tranfactions Mr. Swinton informed us that NI. LUFIUS, whose name occurs on this denarius, was probably one of the Italian generals in the Social war. In the prefent article he haftens to acknowledge and rectify his mistake, in wrongly decyphering two or three crippled Samnite Etrufcan letters at the tail of the infcription; and now declares his opinion that this fuppofed old foldier was really the Merrifs, Merrix, or Meddix, or at least one of the

[ocr errors]

* And yet the nitrous acid has a lefs degree of affinity to tin than to copper, the latter of which it diffolves, while it, only corrodes the former; perfectly dephlogisticating it, or reducing it to a compleat calx. Its violent action on the tin therefore, though already faturated with the copper, is, we apprehend, to be attributed to this circumftance; that though it has a very inconfiderable degree of affinity to the metallic earth of the tin, it attacks this metal with violence on account of its very ftrong attraction of phlogiston; a principle which is known to adhere to tin very laxly.

5

two

« ElőzőTovább »