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tfofc Caufes fecm to have their Effta : Thofe Slights at- tended with large Worms or Caterpillars, feem hatch'd by the Eaftcrn Winds ; and thofe others, which only produce the fmall Infers, that occafion the Curling of the Leaves of Trees, may proceed from Swarms of 'em, either ready hatch'd, or in (he Eg**, brought with the Wind. The Coldnefs of thofe Winds he fhews to be no Objection againft their being fitted to hatch Infects ; different Infers requiring vaftly different degrees of Heat. To this he Ihews that every Infect has its proper Plant, or Tribe of Plants, which it naturally requires for its Nourifhment, and will feed on no other ; and in which, therefore, it lays its Eggs : 'Tis no wonder then, that one kind of Tree fhculd be infeftcd, and all the reft efcape. That Wind, v.g. which brings, or hatches, the Caterpillars on the Ap- plc-Tree, will not infect the Pear, Plum, or Cherry ; be- caufe, were the Shoals of Infects natural to the Apple, to light on thofe other Trees mention'd, they would either want their proper Matrix to hatch in; or, were they ready hatch'd, would perifh for want of proper Food. So that 'tis morally impoffible, all kinds of Plants fhould be blighted at the fame time, unlefs the Eggs of every kind of Infect natural to each Tree, could be brought at one time with the Wind ; or, that an Eafterly Wind cou'd contain in it at once, as many different Degrees of Cold, or Heat, as wou'd be rcquir'd to hatch and maintain each different Oafs of Infects. Nor is it any Objection, that in Slights there are not frequently any Animals immediately perceivable. By the Microfcope, we difcovcr Animalcules a Million of times Jefs than the fmalleft which comes under ordinary Notice: Thefe, the gentleft Air may be conceiv'd capable of blow- ing from Place to Place ; fo that 'tis no wonder if they be brought to us from the remoteft Regions, efpecially the North-Eaft Parts of Great lartary, &c. where the Cold is intenfe enough to give 'em Life ; and from whence there is not Sea enough, by the Warmth and Saltnefs of whofe Vapours they may be fuffbeated. Thofe brought from the North-Eaft Parts of America, may be probably deftroy'd by parting the vaft Atlantkk Ocean, which may be the realon why the North- Weft Wind is not fo infectious.
What confirms this Doctrine of Slights is, that the more knowing among Country-People, while the Eaftern Winds blow, ufo to guard againft Slites by burning Heaps of Weeds, Chaff, and other Combuftibles, on the Wind-fide of their Orchards, that the Smoke may either poifon the Infects, or their Eggs, as they pafs along. It may be ad- ded, that thefe Fires are often made with good Succefs, to deftroy the Caterpillars, even after they were hatch'd, and had began to devour the Trees. Another Method of prefer- ving Trees (romSligbts is,by fprinkling Pepper-Duft ; which, 'tis laid, is prefent Death to all Infects, and even all Animals. Corn is liable to Slights like other forts of Grain. The Slight of Wheat, call'd Smut, is prevented by waffling the Wheat in three or four Waters, ftirring it well all the time, and skimming off the light Wheat, then fteeping it 30 or 40 Hours in Water impregnated with Salt, with the Addi- tion of Ibme Alum, till it be capable of fuftaining a Body of twice the fpecifick Gravity of an Egg ; when taken out, fome flack'd Lime is iifted on it, to dry it fit for fow- ing the next Day : Such a Procefs fecures the Grain from being infeftcd with any kind of Vermine.
BLINDNESS, a Privation of the Senfation of Sight, ariiing from a total Depravation of the Organs thereof, or an involuntary Obftruction of their Functions. The Caufes oiSlivdnefs are various; proceeding from Cataratts, Gutta Serena's, &c. which fee. Aldrovandus tells us of a Sculptor, who became hl'md at 20 Tears of Age, and yet 10 Years after made a perfect Marble Statue of Cofmo II. de Medichz, and another of Clay, like Urban VIII. Sar- thvlin tells us of a blind Sculptor in (Denmark, who diftin- guifh'd perfectly well, by mere Touch, not only all Kinds of Wood, but all the Colours ; and F. Grimaldi gives us an Inftance of the like kind, befide the blind Organift late- ly living in 'Paris, who is faid to have done the fame. F. %aha gives abundance of Inftances of the amazing Sagacity of blind People, in his Oculus Artificialis. The Author of the EmbafTy of D. Garcia de Silva Figueroa into TerJIa tells us, that in feveral Parts of that Kingdom are found vaft Numbers of ' Hi?id People of all Ages, Sexes, and Con- ditions ; by reafon of little Flies which prick the Eyes and Lips, and enter the Noftrils, carrying certain Slindnefs with 'em. See Sight.^
The Chymifts fay their Veffels are Mind, which have no Opening but at one Side. See Coecum.
BLINDS, in Fortification, Defences made of Wood, or Branches interwoven and laid a-crofs between two Rows of Stakes about the Height of a Man, and four or five foot a- part. They are ufed particularly at the Heads of Trenches, when they are extended in Front towards the Glacis ; fer- ving to fhelter the Workmen.
BLISTER, See Vesicatory.
BLOCK, a Piece of Marble, as it comes out of the Quarry, e'er it has affum'd any Form from the Workman's Hand. See Marble.
Block, in Falconry, the Perch whereon the Bhd of Prey is kept. This is to be cover'd with Cloth.
BLOCKADE, the Siege of a Place, intended to be ta- ken by Famine; wherein all the Paffages, and Avenues, are feiz'd, and fhut up, fo as no Supplies of Provifion can be brought in. A Stockade, in ftrictnefs, is no regular Siege $ inafmuch as there is not any Defign of an Attack. A Block- ade is form'd by the Cavalry. The Word is fometimes al- fo ufed at the Beginning of a Siege, when Forces are lent to feize the principal Avenues, where the Scjiegers intend to fix their Quarters. It comes from the German Slochus y a wooden Houfe ; or from the Gaulijh Sicca!, Barricade : Others derive it from the Latin bucularc, to fhut up the Paffage.
BLOCK-LAND was formerly that which we now call Freehold Land, or Land held by Charters ; and it was by that Name diitinguifh'd from Folk-land, which was Copy- hold Land.
BLOCKS, a-board a Ship, are Pieces of Wood in which the Shivers are placed, and wherein the Running-Ropes go: Of thefe, fome are fingle, fome double; and lbme have three, four, or five Shivers in them. They are na- med and diftinguifh'd by the Ropes they carry, and the Ufes they ferve for.
BLOM ARY, the firft Forge in an Iron-Mill thro which the Metal paffes after it is melted out of the Mine. See Ikon.
BLOOD, a warm, red Liquor or Humour, circulating, by means of Arteries and Veins, through every Part oi the Body. While in its Veffels, it appears to the naked Eye, uniform and homogeneous; but, when let out and cold, feparates fpontaneoully into two different Parts ; the one red and fibrous, which coheres into a Mafs, and is call'd the Cruor ; the other thin and tranfparent, which retains its Fluidity when cold, and, being fuppos'd fpecifically hea- vier than the other, fuftains and beats it up, and is call'd the Serum. The Proportion of the Serum to the Cruor, Dr. (Drake makes at a Medium, as one and an half to one : But Mr. Soyle, more accurately, makes the Serum f * of the whole Shod $ and Dr. Jurin || of the whole Weight, or £ of the Bulk.
By the Microfcope, the Shod appears to confift of little red Globules, fwimming in an aqueous Liquor, fuppos'd to be the Cruor and Serum, that appear fo diftinct when let out. M. Lee-wenhoeck computes thefe Globules to be twenty five thoufand times fmaller than the fmalleft Grains of Sand j and Dr. Jurin makes 'em ftilllefs. Upon an accurate Men- furation, he found the Diameter of one, equal to ™a^ of an Inch, or * T4 - of an ordinary Hair of the Head. Dr. (Drake thinks, that tho the rapid Motion of the Shod may- make the Cruor appear round, and perhaps, by a kind of Whirling, or Rotation, really convolute 'em ; yet that their Figure is not naturally Globular, when let out, as appears from their Cohefion, or hanging together in a Lump; which fpherical Bodies, touching in a very few Points, are not apt to do : But, on the contrary, this Property, he thinks, argues an Implication of their Fibres within one another : Which is confirmed by what Dr. Adams obferv'd by his Microfcope, viz. that immediately after Emiffion of Shod, 'tis fo far from exhibiting any red Globules, that it appears to con- fift of infinite Branches, running in no certain Order, and varioufly colour'd.
By a Chymical Analyfis, the Shod is found to confift of (Phlegm, as the Ban's or Vehicle of Volatile Salts ; of 0/7, which, by fome nice Examiners, has been found of two Kinds ; and of Caput mortuum, or Earth ; which, tho it may confift of divers Subftances, eiTentially different from each other, yet all we get out of it is a little fix'd Salt. From the belt Experiments in this kind it appears, that in feven Ounces of human Blood, there are five Ounces two Drachms of Phlegm, three Drachms of a fubtiie, fpirituous Oil, two Grains of a thicker Oil, two Drachms of Salt, and about two of Earth. Dr. Jurin adds, that the Serum t upon a Chymical Analyfis, exhibits a great deal of Phlegm, and of the other Principles a fmall Quantity ; and, on the contrary, the Cruor yields lefs Phlegm, but the other Prin- ciples much more copioufly than the Serum. From which Data he concludes, that the Globules confift of fome Phlegm united with the Oil and Salts, and a fmall Quantity of Earth; but in what Proportion, and how, and in what Parts they are form'd, ££?c. is not determin'd. Indeed, it muft be confider'd, that the Principles which the Chymifls thus produce feparate, may poflibly be much alter'd by the Fire. Thus, 'tis paft doubt, the Oils drawn from the Shod by Fire, are vaftly different from the natural Oil which cir- culates with the Shod. To which may be added, that the Caput mortuum remaining after Diftillation, may, poffibly, be a new Production, which had no Exiftence under any Form refembling that in the Shod.
The
