rare and unconfined air, as we often fee during the autumnal evenings. But it is far otherwife when these fermenting matters are contained in the denfe body of a cloud: the great refiftance they then meet with occafions an equal power of re-action, which is fpent wholly on the body of the cloud and ambient air; which air, by this means, having it's vibrations excited in the highest degree, occafions thofe loud reports from the upper regions, and expanding over all the inferior parts of the atmosphere, propagate thefe awful founds which we call Thunder. A Thunder Bolt, being a phænomenon of the moft folemn kind, the confideration of it fhould certainly fill every ferious mind with awe, when the many dreadful effects frequently produced by it are confidered. Initant death is the immediate effect of it's ftroke in animals, the ftrongeft trees are rent and torn afunder, the fineft buildings are at once demolished, and the hardeft metals in a moment diffolved! Such are the effects of the greatest and most formidable powers in nature; and they have lately been bat too evidently difplayed. The fubftance of these bolts confifts of a compact and undifolved body of ignited matter, which not having fufficient time to explode in the air, is darted, with the velocity of light itfelf, to the objects.on the furface of the earth, which it ftrikes with an inconceivable and irrefiftible force, deftroying at once the nature and texture of every thing that ftands in it's way. The matter of lightning may be refolved into three different ftates. First, that in which it only explodes, and flashes away without proving deftructive. Secondly, when it explodes with greater force and density: then it's effects are often but too fenfibly felt at a distance, ftriking the unhappy fpectator with blindness, and fetting fire to ftacks of corn, houfes, &c. And, thirdly, that of the thunder-bolt. VOL. III. RAIN. THE alteration in the weight of the air is the general cause of rain; by which means the clouds defcend, intermix, and thereby become much heavier: their weight now forcing the aqucous particles together, they attract each other, and the cloud becomes liquified, much after the fame manner as a heated fteam or vapour condenfes, or runs into drops, against any cold furface. The water of the cloud, as falt as it is produced by this coalefcence and condenfation, being heavier than the air, must neceffarily diftil through it, and defcend in drops of rain; and thus, from the bafis or lower part of the cloud, proceed thofe fhowers which the bounty of Providence beftows on every part of the earth, as there is occafion or neceffity for them. The winds are another general caufe of rain, driving the clouds together, forcing them to coalefce, condenfe, and become heavier, and therefore to fall in rain. Thofe winds which blow from the ocean, (as the fouth and weft) bring large recruits of vapours to the clouds, and are therefore more likely to produce rain than the north and north-east winds, which blow from the land, and generally difperfe the vapours, and drive the clouds away. THE RAINBOW. AMONG the various meteors which refult from the reflection of light, the Rainbow is certainly the most pleafing and extraordinary: it's colours not only charm the eye with the mildnefs of their luftre, but convey de light to the mind of the fpectator, by the profpect of fucceeding ferenity which they enfure. This beautiful meteor is only feen when the fpectator turns his back to the fun, the rain at the fame time falling on the oppofite fide. It's colours, beginning from the infide of the arch, are violet, indigo, blue, green, yellow, orango, and red, being the delightful fhades of the prifm. We often fee an external rainbow, with colours lefs vivid than the firft, and ranged in an oppofite order, beginning from the under part, red, brange, yellow, green, blue, indigo, violet; fometimes we fee half, fometimes an whole bow; frequently one, very often two, and even three have been feen. Dr. Halley gives an account of his having obferved fuch a triple bow at Chefter; and many others have likewife feen them. The difference between the bows is, that in the internal bow each drop receives the rays of the fun on it's upper furface; whereas, on the contrary, in the great external bow, each drop receives the fun's rays at it's bottom, from whence the ray being twice refracted, and twice reflected, it comes to the fpectator's eye with diminished luftre, and in an inverted order. If, with our backs turned towards the fun, we fquirt water from our mouths, or look at the fcattering drops of a fountain or water-fpout, the rainbow will appear pretty accurately imitated on the difperfed drops; and we fhall generally, at the fame time, diftinguifh two rainbows. Befides the common rainbow, occafioned by the rays of the fun, there is fometimes alfo a lunar one, formed exactly in the fame manner, by the bright beams of the moon ftriking on the bofom of a shower. This meteor, Ariftotle boats, was Firft remarked by himfelf; and he affures us, that, in his time, fuch a rainbow was feen, with the colours extremely lucid. Similar meteors have beeen frequentIy obferved fince; and, among our own countrymen, Mr. Thoresby has given the defcription of one in the Philofophical Tranfactions. The lunar rainbow which this laft gentleman obferved, was equally admirable both for the beauty and the fplendor of it's colours: and it lafted about ten minutes, when the view was intercepted by a cloud. COLD AND FROST. COLD being a comparative term, fignifies nothing more than that leffer degree of heat ufually called moderate; and it is well known that fome bodies will liquify with one degree of heat, and become fixed with another. With one degree of warmth, water will appear in a fluid ftate; with a lefs, it's particles will be found to be fixed, congealed, or frozen. Thus the vapours, in a warm air, are in a fluid ftate; and when condenfed by the coldness of the evening, they defcend, adhere to the piles of grafs in the liquid form of pearly drops, and are in that ftate denominated Dew: but thefe very particles, in a ftill colder air, will be fixed, and, while they are floating in the air, make what is termed a Rimy Fog, or Frozen Mift. Defcending upon the grafs, and the twigs of fhrubs and trees, they make a beautiful incruftation, called a Hoar or White Froft, in contradiftinction to another fort, termed the Black Froft, only because it does not appear white; and this Black Froft differs from the other, because it is not accompanied with a mift or fog. SNOW. THE particles of all falts naturally running together, conftitute fome particular form; and as they are in themfelves tranfparent, and clear as glass or cryftal, this natural action of fhooting into thofe forms is termed Crystallization; and the particles fo combined and configurated are called the cryftals of fuch and fuch falts or metals. Water being an infipid, fluid falt, in the upper region of the air, where the conftituent parts of nitrous falts abound, the difpofition to freezing or congelation is very great in the winter feafons, when the atmofphere is much lefs heated by the fun's rays than during thofe of the fummer; and the aqueous particles mixing with nitre, immediately shoot into cryftals, and form the original parts of fnow, whofe figure is truly wonderful; for, from one point, as a centre, they irradiate into fix different but very beautiful parts, more or lefs connected, and variegated with an appearance of a vegetable nature. Thefe Thefe fnowy cryftals, being of an hexagonal and ramous form, are apt to hitch into and hang upon one another, till they compofe a body too heavy to be. fupported by the air, when they defcend in the shape of Flakes of Snow, which are smaller or larger according to the degree of cold which forins them. Thefe flakes, by reafon of their weight, defcend, with a gentle and irregular motion, through the air; fo that a fhower of fnow (though common to us, and therefore not much regarded) is in itself a moft beautiful thing, and beheld by the natives of fouthern climes, on their arrival in this country, as one of the moft extraordinary and amazing phoenomena of nature. HAIL. It is obfervable, that fhowers of Hail feldom fall except when the air is heavy, and the vapours afcend to a great height in it; and this during the fummer months, when hail-ftorms are much more frequent than in the winter feafon. The cold, in the higher regions of the air, being much more intenfe than in the lower, a much greater quantity of nitre is lodged in the former than in the latter, caufing a more immediate and ftronger congelation of the aqueous particles, and binding them firmly into bodies of ice of various magnitudes, according to the degrees of cold. PHILOSOPHICAL TRANSACTIONS. ACCOUNT OF A CHILD WHO HAD THE SMALL-POX IN THE WOMB. IN A LETTER FROM WILLIAM WRIGHT, M.D. F.R.S. TO JOHN HUNTER, ESQ. F.R.S. SIR, I Have read with much pleasure and information Mrs. Ford's cafe, which you publifhed in Phil. Tranf. Vol. LXX. From the facts you have adduced, it amounts to a certainty, that her foetus had received the variolous infection in the womb. This induces me to lay before you. fingular cafe that fell under my care fome years ago. I am forry [ cannot be more particular, having unfortunately loft all my books and my notes of practice of this cafe and feveral others, by the capture of the convoy on the 9th of laft August. In 1768, the fmall-pox was fo general in Jamaica, that very few people efcaped the contagion. About the middle of June, Mr. Peterkin, merchant at Martha-brae, in the parifh of Trelawney, got about fifty new negroes out of a fhip; foon af ter they landed, feveral were taken ill of a fever, and the fmallpox appeared; the others were immediately, inoculated. Amongst the number of thofe who had the difeafe in the natural way, was a woman of about twenty-two years of age, and big with child. The eruptive fever was flight, and the fmalf-pox had ap-. peared before I faw her. They were few, diftinct and large, and fhe went through the difeafe with very little trouble, till on the fourteenth day. from the eruption fhe was attacked with the fever, which lafted only a few hours. She was, however, the fame day taken in labour, and delivered of a female child with the fmall-pox on her whole body, head, and extremities. They were diftin&t and very large, fuch as they commonly appear on the eighth or ninth day in favourable cafes. The child was small and weakly; fhe could fuck but little; a wet-nurfe was procured, and every poffible care taken of this infant, but he died the third day after fhe was born. The mother recovered, and is now the property of Alexander Peterkin, Efq. in St. James's parish. In the courfe of many years practice in Jamaica, I have remarked, that where pregnant women had been feized with the natural fmall-pox, or been by miftake inoculated, they generally mifcarried in the time of, or foon after, the eruptive fever; but I never faw any figns of fmall-pox on any of their bodies, except on the child's above-mentioned. C 2 I am, &c. NATURAL NATURAL HISTORY OF THE IN- Lacca. About the middle of March, the cells are compleatly formed, and the infect is in appearance an oval, fmooth, red bag, without life, about the fize of a fmall cuchanical infect, emarginated at the obtufe end, full of a beautiful red liquid. In THE head and form one uniform, oval, compreffed, red body, of the fhape and magnitude of a very fmall loufe, confifting of twelve tranfverfe rings. The back is carinate; the belly fat; the antennæ half the length of the body, filiform, truncated, and diverging, fending off two, often three, delicate, diverging hairs, longer than the antennæ. The mouth and eyes could not be feen with the naked eye. HE head and trunk of the Coc- October and November we find about The tail is a little white point, fending off two horizontal hairs as long as the body. It has three pair of limbs, half the length of the infect. I have often obferved the birth of thefe infects, but never could fee any with wings; nor could I find any diftinction of fexes, or obferve their connubial rites: nature and analogy seem to point out a deficiency in my obfervations, poffibly owing to the minutenefs of the object, and want of proper glaffes. This infect is defcribed in that ftate in which it fallies forth from the womb of the parent in the months of November and December. They traverse the branches of the trees upon which they were produced for fome time, and then fix themselves upon the fucculent extremities of the young branches. By the middle of January they are all fixed in their proper fituations, they appear as plump as before, but fhew no. other marks of life. The limbs, antennæ, and fete of the tails, are no longer to be feen. Around their edges they are environed with a fpiffid fubpellucid liquid, which feems to glue them to the branch: it is the gradual accumulation of this liquid which forms a compleat cell for each infect, and is what is called Gum twenty or thirty oval eggs, or rather young grubs, within the red fluid of the mother. When this fluid is all expended, the young infects pierce a hole through the back of their mother, and walk off one by one, leaving their exuviæ behind, which is that white membranous fubftance found in the empty cells of the Stick Lac. The infects are the inhabitants of four trees. 1. Ficus Religiofa, Linnæi. In Hindoftan, Pipul. Banyan Tree. 2. Ficus Indica, Linnæi. In Hindoftan, Bhur. Banyan Tree. 3. Plafo Hortus Malabarici. the natives, Prafo. By 4. Rhamnus Jujuba, Linnæi. In Hindoftanick, Beyr. The infects generally fix themfelves fo clofe together, and in fuch numbers, that I imagine only one in fix can have room to compleat her cell: the others die, and are eat up by various infects. The extreme branches appear as if they were covered with a red duft, and their fap is fo múch exhaufted, that they wither and produce no fruit, the leaves drop off, or turn to a dirty black colour. Thefe infects are tranfplanted by birds: if they perch upon thefe branches, they muft carry off a-number of the infects upon their feet to the next tree they rest upon. It is worth obferving, that these fig-trees, when wounded, drop a milky juice, which inftantly coagulates into a vifcid ropey fubftance, which, hardened in the open air, is fimilar to the cell of the Coccus Lacca. The natives boil this milk with oils into a bird-lime, which will catch peacocks, or the largeft birds, A red medicinal gum is procured by incifion from the Plafo Tree, fo fimilar fimilar to the Gum Lacca, that it may readily be taken for the fame fubflance. Hence it is probable, that thofe infects have little trouble in animalizing the sap of these trees in the formation of their cells. The gum lacca is rarely feen upon the Rhamnus Jujuba; and it is inferior to what is found upon the other trees. The gum lacca of this country is principally found upon the uncultivated mountains on both fides the Ganges, where bountiful nature has produced it in fuch abundance, that were the confumption ten times greater, the markets might be fupplied by this minute infect. The only trouble in procuring the lac is in breaking down the branches, and carrying them to market. The prefent price in Dacca is about twelve fhillings the hundred pounds weight, although it is brought from the diftaut country of Affam. The best lac is of a deep red colour. If it is pale, and pierced at top, the value diminishes, because the infects have left their cells, and confequently they can be of no ufe as a dye or colour, but probably they are better for varnishes. This infect and it's cell has gone under the various names of Gum Lacca, Lack, Loc Tree. In Bengal, La; and by the English it is diftinguished into four kinds. 1. Stick Lac, which is the natural ftate from which all the others are formed: 2. Seed Lac is the cells feparated from the sticks. 3. Lump Lac is Seed Lac liquified by fire, and formed into cakes. 4. Shell Lac is the cells liquified, ftrained, and formed into thin tranfparent laminæ, in the following manner. Separate the cells from the branches, break them into small pieces, throw them into a tub of water for one day, wafh off the red water, and dry the cells, and with them fill a cylindrical tube of cotton cloth, two feet long, and one or two inches in diameter; tie both ends, turn the bag above a charcoal fire; as the lac liquifies, twift the bag, and when a fufficient quantity has tranfuded the pores of the cloth, lay it upon a fmooth junk of the plantain-tree, (Mufa Paradifiaca, Linnai) and with a ftrip of the plantain leaf draw it into a thin lamella;. take it off while flexible, for in a minute it will be hard and brittle. The value of shell lac is according to it's transparency. This is one of the moft ufeful infects yet difcovered. The natives confume a great quantity of fhell lac in making ornamental rings, painted and gilded in various taftes, to decorate the arms of the ladies; and it is formed into beads, fpiral and linked chains for necklaces, and other female orna ments. For Sealing-wax. Take a flick, and heat one end of it upon a charcoal fire; put upon it a few leaves of the fhell lac foftened above the fire; keep alternately heating and adding more fhell lac, until you have got a mafs of three or four pounds of liquified fhell lac upon the end of your tick*. Knead this upon a wetted board with three ounces of levigated cinnabar, form it into cylindrical pieces; and, to give them a polish, rub while hot. with a cotton cloth. For Japanning. Take a lump of fhell lac, prepared in the manner of fealing-wax, with whatever colour you pleafe, fix it upon the end of a' ftick, heat the polished wood over a charcoal fire, and rub it over with the half-melted lac, and polish, by rubbing it even with a piece of folded plantain-leaf held in the hand; heating the lacquer, and adding more lac as occafion requires. Their figures are formed by lac, charged with various colours in the fame manner. In ornamenting their images, and religious houfes, &c. they make use of very thin beat-lead, which they cover with various varnishes, made of lac charged with colours. The preparation of them is kept a fecret. The leaf of lead is laid upon a smooth iron In this manner lump lac is formed from feed lac, heated |