ber, as a foffil, is unknown, but it is probably of a mineral fpecies, being a kind of bitumen, that was once in a fluid or very soft state, as is evinced by the number of extraneous objects obferved in it, fuch as ftraws, or small infects, and that it was hardened into it's prefent ftate by a mineral acid of the nature of fpirit of fulphur, oil of vitriol, &c. The native colour of amber is yellow; it is tranfparent to a confiderable degree, of a hard, compact confiftence, admits of a very high polish, and is of an inflammable nature, and supposed to be foluble in certain menftruums. Tourmalin, is a gem, or jewel, which the Dutch artifts firft difcovered to poffefs an electric power; for, in heating it by grinding and polishing, they obferved that it attract ed afhes, and other light bodies near it. As electricity is of two forts, amber poffeffes one, and glafs the other: but the tourmalin poffeffes them both; or, rather, both forts may be excited in it, the pofitive on one fide, and the negative on the other. The mode of exciting electricity, in amber and glass, is by rubbing; but, in the tourmalin, by heating it only. Thus, if it be heated by fire or hot water, one fide will attract and the other repel light bodies; but it is of too fmall a bulk to afford thefe powers in quantities and ftrength fufficient for practical uses. The Magnet, or Loadstone, is a foffil which has the fingular property of attracting and repelling iron, but no other body, unless it be the fame in fubftance. There are two parts in every magnet, called it's poles, from one of which iffues an attractive, and from the other a repulfive power. This is univerfally the cafe in every piece of magnet, great or fmall; and it's power is communicable to iron, but to no other fubftance. The magnetic iron is then called an artificial magnet, and acts in every refpect like the natural one. This power circulates from one pole to the other, on every fide; therefore, every magnet is in the centre of a magnetic vortex or atmosphere of it's own power. Every magnet, when in a condition to move freely, will place itself in one and the fame pofition with refpect to the points of the compafs, for many years together, without any fenfible alteration. If an artificial magnet, or what is ufually called a magnetic needle, has a brafs cap fixed in it's centre, with a conical hole on the lower fide, by which it may be fufpended on the point of a pin in the centre of a circle divided into thirty-two equal parts, then this needle being truly equipoifed, will, after feveral vibrations, fettle itself in a pofition directed to one of thofe divifions on the circle, called the thirty-two points of the compafs. The noble art of navigation depends wholly upon the magnet, or the variation of the needle it occafions. This variation of the needle is in itself variable, the fituation and direction of the needle in any one place gradually altering, fo as, in a courfe of years, to become fenfible: thus, at London, the variation was a whole point to the east about a century ago; afterwards it veered to the north, and at laft came precifely into the plane of the meridian of London, fo that then there was no variation at all. Ever fince that time it has been veering weftward, and is now more than twenty-one degrees to the weftward of our meridian. But this proves no impediment to navigation; because, if the quantity of it be known at any time, there is nothing more requifite. In order to render a needle magnetical, the north part must be made fomewhat lighter than the fouthern, for otherwife it would not ftand level, but dip below the horizon: but this dipping of the needle, and the variation, tend to the fame thing; only the former is in a vertical plane, while the latter is in a horizontal one. needle dips with us about feventy degrees below the horizon; but this dipping is of no ufe to mariners, be caufe made in the plane of the meri. dian. In communicating this virtue to the needle, three things are very carefully to be obferved: first, that it be touched by an artificial magnet, as the power is much greater than in a natural one; fecondly, that each Z 2 The end end of the needle be touched at the fame time, the north end of the needle by the fouth pole of the magnet, and the fouth end of the needle by the north pole of the magnet; thirdly, that, in touching, the magnets are always to be drawn from the middle to the ends of the needle This laft caution is particularly neceffary, becaufe what is gained by drawing the magnet one way, is loft by drawing it the other; and the fecond precaution is alfo neceffary, because the fame polar virtue in the ends of the magnet and needle makes them repel each other, and confequently the end of the needle that was touched by the fouth pole of the magnet will be repelled afterwards by it. Though there must be a fomething to actuate the needle at fea, nothing that is abfolutely invifible can affect the needle but magnetifm: it is therefore evident that nothing befides the earth itself can be the magnet in queftion; fince a magnetic vortex from the earth alone can be fufficient to account for the phænomena of the needle on every part of it's furface. But the poles of it's magnetifm can never be in the poles of the globe, or in the ends of it's axis, because in that cafe there could be no variation of the needle, but a dipping only. Neither can they be fixed in any other part of the earth's furface, for in fuch cafe there would be a conftant variation in the fame place. There muft, therefore, neceffarily be an internal magnet in the earth, which is moveable, and conftantly altering it's pofition, or direction of it's axis. The ftrength of natural magnets is estimated by their blacknefs, hardnefs, and the weight they are capable of lifting compared with their own. Thofe which will take up twenty times their own weight are reckoned very good. Others will take up thirty times their own weight, but fuch are rarely to be met with. and Crystal is the fairest and most delicate fofil produced by the earth, and of the greatest celebrity among philofophers, as well as naturalifts, for it's fingular and amazing property of a double refraction of light, It is, in it's common appearance, much like other crystals, pellucid and clear as water: it alfo grows, like them, from the hardelt rock and stone, in form of hexagonal pyramids, with very sharp points. points. When thefe large crystals are broken off the ftone, and into many different pieces, each piece, whether large or fmall, is precisely of the fame form, or quadrangle, hav ing fix fides, and the two oppofite ones exactly parallel to each other. Every piece has the fame form and attributes. It has the peculiar property of double refraction; so that a beam of light, inftead of paffing through it fingly, and entire, as in glafs, is divided into two or more beams of light; and the object viewed by the fame light is divided in like manner into two or more objects. Naturalifts have hitherto confidered only two refracted beams in this cryftal; but it has been found, on grinding and polishing feveral pieces into the form of prifms, that the refraction is not only double, but manifold; and that a variety of prifms produce a great variety of refractions, and prefent as great a number of images to the view of one and the fame object. Some fhew but two images, others three, four, fix, twelve, fixteen, and even twenty; which demonftrates that there is a refraction of one beam of light into as many different parts. Each image is at the fame time tinged with a variety of prifmatic colours, fome of which are intenfely ftrong and bright when the object is luminous, as the window, a candle, or the fun. The Afbeftos, or Amianthus, is poffeffed of very fingular and extraordinary qualities; and that strange and furprifing one, peculiar to this foffil, by which it refifts the force of the ftrongeft fire, renders it a fubject of the greatest admiration. One fide of the Afbeftos exhibits nothing remarkable in it's appearance; but the other has a delicate and beautiful fur, face which appears like the fineft green filk or fattin, or rather a fort of petrified cotton or filk; filky filaments feeming to run through the whole length, and to compofe the entire furface, The firmness of it's texture, and the natural natural polish of it's fibres, gives the whole a delightful glofs; and when thofe fibres, or filky filaments, are raised up with the point of a needle, they appear of a very different form and colour, resembling an affemblage of the fofteft filky fubftance, and whiter than the pureft cotton; fo that they might easily be wrought into a web of fine filk ftuff or cloth. There is much of this foffil in England, but it is of an inferior nature, and confequently of very little value; the best foffils of every kind, except Mundics, are indeed met with in warm regions. Mundic is a fpecies of that fort of marcafite which is chiefly remarkable for it's great variety of the most intenfe, glorious, and glowing colours, any where to be found in nature. Mundic may be faid to wear the richeft livery of the Deity, there being no bodies of the animal or vegetable clafs whofe refulgence is comparable to that of the finest fort of mundic. It's refplendent colours are innate and permanent, and are heightened to an aftonishing degree. They have the greateft variety of all prifmatic colours in deeper dyes than in any other bodies with which we are acquainted; viz. the red, orange, yellow, green, blue, indigo, purple, violet, and every other known colour. The more they are magnified, the ftronger they appear; and, when they are properly placed in the opake folar microfcope, and magnified about forty times in diameter, they exhibit fuch fcenes of glory as are perfectly ineffable, and cannot be conceived without viewing them. THREE ORIGINAL LETTERS which you mention concerning the 21, 57, 16, 3, 44, 5, 19, 53, 33, 205. 222, 208, and that which is intended after; but whofoever will join with me must come to my grounds, a chief part whereof is the including my friends, without which I affure you no agreement fhall be made; this army fpeaks me very fair, which makes me hope well, but it must be their actions, not bare words, which will make me trust them: I have declared for my going to Richmond, from which nothing fhall (by the grace of God) divert me (if the two Houfes do not recede from their votes) but direct force, which I hope the army will not offer to do, for if they mean well, this my journey will be available to them, and, whatever they intend forcing of my perfon will do them more harm than good. I defire that this may ferve for those two honest men whofe letters came with yours, defiring them, as alfo all my other friends, not to engage particularly to either party, but ftay to declare as I fhall do, for I am neither independant nor prefbyterian, but shall be moft for them who are moft really for the peace of the kingdom, according to the known laws. So farewell. LETTER II. C. R. 7 AUG. Acknowledge that what 222: 1273 fent to you for the loan of your cypher was by my directions, it being to that end as was mentioned, and that the ticket was mine, which I thought fufficient to have made you done what is required; but I confefs that too much caution is a moft excufable error, and I will not fay but OF KING CHARLES THE FIRST, To that my direction was too laconic; FLEETWOOD, LATELY PRESENTED TO THE BRITISH MUSEUM BY A DESCENDANT OF BISHOP FLEETWOOD. LETTER I. NEWMARKET, 21 JUNE 1647. I Thank you for your cypher and your advertisements, and fhall not miflike if that fhould happen however I defire you to lend 222, 127, cypher, as 65, 6, 18, 11, 367, defired as being a perfon whom you may truft. This I have written before I have decyphered the latter part of your letter, that mine may be no longer ufelefs to 222, 127: fo farewell. If there be any thing to answer to yours, you fhall learn from me very fhortly. LETTER LETTER III. 7 AUG. 1647. HIS morning I anfwered the former part of your yesterday's letter, in which I find another mistake, after I had decyphered the latter, for I fee you thought T. A. had written the note which was fent you for the loan of your cypher, but I affure you it was 367, 184, 108, wherefore again I defire you to lend it 166, who fends you this; and hereafter, when my name is used to you, of which you make any doubt, fend immediately to me and none elfe. So farewell. C. R. PHILOSOPHICAL TRANSACTIONS. I ANIMALS TO PRODUCE COLD. (Concluded from Page 105.) Shall now endeavour, from the preceding facts, to explain what appear to me to be the true caufes of the cold produced by animals when placed in a medium, the temperature of which is above the ftandard of their natural heat. In a work which I fome time ago laid before the public, having attempted to prove, that animal heat depends upon the feparation of elementary fire from the air in the procefs of refpiration, I obferved, that when an animal is placed in a warm medium, if the evaporation from the Jungs be increafed to a certain degree, the whole of the heat feparated from the air will be abforbed by the aqueous vapour. From the experiments on venous and arterial blood, recited in the third fection of that work, it appears, that the capacity of the blood for containing heat is fo much augmented in the lungs, that, if it's temperature were not fupported by the heat which is feparated from the air, in the pro- It follows, that the quantity of heat given off by the blood in the *It is of no confequence in the above argument, whether we fuppofe, with Dr. Priestley, that the alteration of colour in the blood depends upon it's combination with phlogifton in the capillary arteries, or maintain with fome other philofophers, that this alteration arifes from a change produced in the blood itself by the action of the vefiels; it is fufficient for our purpofe to affume it as a fact, which, I think, has been proved by direct experiment, that, in the natural state of the animal, the blood undergoes a change in the capillaries, by which it's capacity for containing heat is diminished; and that in a heated medium it does not undergo a fimilar change. capillaries capillaries will not be equal to that which it had abforbed in the greater veffels, or pofitive cold will be produced. If the blood, for example, in it's paffage to the capillaries, abforb from the greater veffels a quantity of heat as 30 degrees, and if in confequence of it's receiving a lefs impregnation of phlogiston than formerly, it gave off at the extreme veffels a quantity of heat only as 20 degrees, it is manifeft, that upon the whole a degree of refrigeration will be produced as 10 degrees, and this caufe of refrigeration will continue to act while the venous blood is gradually affuming the hue of the arterial, till the difference between them is obliterated; after which it will ceafe to operate. Thus it appears, that when animals are placed in a warm medium, the fame procefs which formerly fupplied them with heat becomes for a time the inftrument of producing cold, and probably preferves them from fuch rapid alterations of temperature as might be fatal to life. Upon the whole, the increafed evaporation, the diminution of that power by which the blood in the natural ftate is impregnated with phlogifton, and the conftant reflux of the heated fluids towards the internal parts, feem to be the great caufes upon which the refrigeration depends. Having found that the attraction of the blood to phlogiston was diminished by heat, it appeared probable, on the other hand, that it would be increased by cold. To determine this, a dog at 100 degrees was immerfed in water nearly at 45 degrees. In about a quarter of an hour a fmall quantity of blood was taken from the jugular vein, which was evidently much deeper in it's colour than that which had been taken in the warm bath, and appeared to me, as well as to feveral other gentlemen, to be the darkeft venous blood we had ever feen. From this experiment, compared with thofe which have been recited above, we may perceive the reafon why animals preferve an equal temperature, notwithstanding the great variations in the heat of the atmofphere, arifing from the viciffitudes of the weather, and the difference of feafon and climate: for, as foon as by expofure to external cold, an unufual diffipation of the vital heat is produced, the blood, in the course of the circulation, begins to be more deeply impregnated with the phlogiftic principle. It will therefore furnish a more copious fupply of this principle to the air in the lungs, and will imbibe a greater quantity of fire in return. In fummer, on the contrary, the reverse of this will take place, lefs phlogiston will be attracted in the minute veffels, and lefs fire will be abforbed from the air. And hence the power of generating heat is in all cafes proportioned to the demand. It is increased by the winter colds, diminished by the fummer heats: it is totally fufpended or converted into a contrary power, according as the exigences of the animal may require. From the changes which are produced in the colour of the venous blood by heat and cold, we may likewife perceive the reason why the temperature of the body is frequently increafed by plunging fuddenly into cold water, and why the warm bath has fuch powerful effects in cooling the fyftem, and in removing a general or partial tendency to inflammation. |