Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/114

 NAT

NAT

weight of the water, as thofeof fuch fifb as have the afiiftance of thcfe air-vcffels. It has been fuppofed by fome, that the motion of fifli in the water depended principally upon the peroral fins, hut this is eafdy proved falie by experiment ; for if the pectoral fins of a fifli are cut off,- and it be again put into the water, it will he found to move forward or fideways, upward or downward, as well as it did when it bad them on. If a fifli he carefully obftiv'd, while jwimming in a balm of clear water, it will be found not to keep thefe pectoral fins conftantly expanded, but only to open them at fuch times as it would flop or change its courfe, this teeming to be their principal, if not their only ufe. The pectoral and ventral fins, in the common fifties of the cathetoplateous orcomprefled form, ferve in the fame manner in the keeping the fiih Hill, and ferve in fcarce any other motion than that toward the bot- tom : fo that this motion of the fifh, which has been generally attributed to their fins, is almoft wholly owing to their mufcles, and to the equipoife of their air-bladder. That the ufe of the peaoral and ventral fins is to keep the fifh fteady and upright in the water, is evident from the confequences of their Lis : if they are cutoff, and the fifh put again into the water, it cannot continue in its erect natural pofture, but ftaggers about, and rolls from fide to fide. The fins of the back and anus are alfo of great ufe to the keeping the creature in its natural po- fition, as is eafily feen by cutting them off, and obferving the motions of the nfh afterwards.

Tho' a great deal depends on the motion of the mufcles of the feveral parts of the body in the jwimming of die fifh, yet the tail, and thofe "mufcles which move the lower part of the body, to which it is affixed, are the great inftrumeuts by . which their fwift motions in the water are performed. The moving the tail, and that part of the body to which it adheres, backward and forward, or fideways any one way, throws the whole body of the fifli ftrongly the contrary way ; and even in jwimming ftrait forward, the motion and direction are both greatly affiftcd by the vibrations of this part, as may be expe- rienced in the motion of a boat, which when impelled for- ward, may be firmly guided by means of an oar held out at its ftern, and moved in the water as occafion directs. The dorfal mufcles, and thofe of the lower part of the body between the anus and tail, are the principal that are ufed in the motion of this part, and thefe are therefore the moft ufeful to the fifh in jwimming. The mufcles of the belly feem to have their prin- cipal ufe in the contracting the belly and. the air-bladder. They have been fuppofed of ufe to move the belly fins ; but there are too many of them for fuch a purpofe, and thcfe fins have each its peculiar mufcle fully fufficient to the bufinefs. The ufe of the tail in jwimming is eafily feen, by cutting it off, and com- mitting the nfh to the water without it, in which cafe it is a moft helplcfs creature. See Ai R-biadder. NAT1VO habendo, inlaw, a writ directed to the flier iff, for a lord who claimed inheritance in any villain, when his villain was run away from him, for the apprehending and reftoring him to the lord. Terms of Law. NATIX, in natural hiftory, a name given by fome old writers

to the nerita. NATRIX, in botany, the name given by Rivinus to a genus of plants, nearly allied to the anonis, and comprehended with it in one genus by Linnseus, under the name of anonis. Rhin. vol. 4. p. 82. Sec jXkst -barrow. Natrix, in zoology, the name of the common or water fnake, called alfo terquata, from the ring about its neck. It is much longer and larger than the viper, and is no water animal, pro- perly fpeaking, but a land one, which being able to fwim very well, often takes the water to hunt about for frogs, which are its principal food. It grows to be much longer and larger than ■ the viper, and does not bring forth live young ones, but great numbers of eggs, which it lays in dunghills, to be hatched by the warmth of the place, or by the heat of the fun. It is very common in bufhy places, and near waters, and in winter finds holes in the banks of ditches, or about the roots of trees, where it lies torpid the whole winter. It has no poifon, and may be fafely taken up and played with, never fo much as attempting to bite. It feeds on many fmall infects, fometimes on vegetable fubftances, and oftener on frogs, mice, &c„

Its back is of a fort of dufky earth colour, and its belly varie- gated with black and a bluifti white, but near the head almoft wholly white, having only a few fmall fpots of black at the fides, the colour growing darker toward the end of the tail ; and near the end, the middle part of all the fcales are black, and their extremities only of a bkiiih white; the whole belly - is covered with long parallel fcales, placed tranfverfely. the back and fides are covered with fmall fcales;, and are variepatcd with feveral ftrcks and fpots of black: there are more than eighty tranfverfe black lines running from the back to the fides ; and befide thefe, two other rows of fmaller, in form of fpots, near the middle of the back. The head is covered with large fcales of a dufkier colour than thofe of the reft of the body, and the upper jaw is white on each fide, with four or five flight lines of black running acrofs it. Its chain is yellow, and is compofed of two large fpots of that colour, placed one on each fide of the neck, or at each angle of the jaws, between which is - placed a large triangular fpot of a deep 6

black, with its top directed toward the tail. It has none of thofe long canine teeth of the viper and other poifonous fer- pents, by means of which the poifon is conve\ed into the ' wound, but only* two rows of fmall ferrated teeth, deftined by nature for no other ufe than eating its food. It may not bejudged improper to have been thus particular in the defcription of this fpecies, as it is well to know what of the fnake kind are, and what are not to be feared ; and as the 'apothecaries and others, for want of thefe characters, often buy this common iiiake under the name of the viper. Rays Syn. Anim. p. 335, 336. NAIRUJVI, or Natron, (CycL) in natural hiftory, the name of the nitre of the antients.

There have been various opinions about the natrum of the an- tients, and fome have been of opinion, that our fait petre or nitre was the fame fubfbnce; but this has been always dif- countenauced by the more judicious. Dr. Hill, who had met with a fait from the fame p.rt of the world whence the an- tients had their natrum, and which anfwered to all the cha- racters they have given of it, defines it to be a fait found fometimes pure, and fometimes fouled with earth, fermenting with acids, and forming flat oblong cryftaUizatlons, with four unequal fides, and two truncated ends'. Thefe were the cha- racters of that fait, and thefe perfectly agree with the accounts we have of nitre in the earlielt age;;, tho' we have none fuf- ficiently accurate to take them all in. And whatever may have been the opinion of fome, that the natrum or nitre of the Hebrews was very early luff, a careful examination of the an- tients proves the contrary, and that this very fait was the nitre both erf the Greeks and Romans, the nitrum and aphrouiirum of Diofcorides, and the nitrum of Pliny. It is found in broad and flat mafies of various fizes, but ufually fmall, and when broken, are found to be compefed of fofciculi or bundles of fmall fibres, of an oblong and flatted figure, and laid but loofely together.

It is naturally of a dufky white ; but is fometimes found of a brown colour, and fometimes of a fine deep red. This is its pureft ftate ;. but befide this, it is frequently found in form of powder mixed with dirt, and rifing in little hillocks on the furface of the ground, it is of an acrimonious pungent tafte, and is more like the alkaline falts produced by burning vege- tables, than any of the native falts. It difiblves in a very fmall quantity of water, and ferments violently with aqua- fortis, or any other weaker acid menltruum. It is found in great plenty in Study, a province in the inner part of Alia, and in many other parts of the eaft, and might be had in any quantities. Perhaps it would be worth confider- mg as a branch of commerce, as it would fupply the place of pot-afhes in the making foap and giafs, as the fame author has tried.

The characters recorded of the nitre of the antients are, 1. That it would ferment with vinegar ; and, 2. That it had an abfter- five quality, Thefe we have from the fcriptures : and the reft were, that it was of an acid tafte ; that it was found native in the eaftern parts of the world ; that it ferved in the place of foap, and that with fand it would make glafs. All thefe pro- perties this fait has; and it may be added, that no other native fait has them ftiU's iHiffc of Foil', p. 386 10389. It is a very remarkable property of this fait, that tho' in itfelf an alkali, and fermenting very violently with acids in its na- tive dry ftate, yet in folution it does not ferment with them at all. If indeed oil of vitriol, or fome other acid, be added to the folution of t.atrum while turbid, that is, while fome of the particles of the fait remain yet whole in it, the two liquors will ferment violently; but if the folution be let by till wholly clear, the fame acid will caufe no effervefcence in it ; but the fame folution, evaporated to a third part, will again fer- ment with that or any other acid, the particles of the fait at that time being got together again, and meeting the acid as in their folid form.

This fait contains a volatile alkali, abforbed from the air, and embodied in it. Its other principle feems a marine fait, which it may receive either from the earth, or from fait fprings or fea water, according to the different places where it is found.

Pliny tells us, that the natrum of Egypt was only found to be produced at thofe times of the year w r hen the dews fell. And iVl. de la Chambrc affirms, that in Egypt, three or four days before the Nile begins to overflow, there always falls a certain dew, which has a fermenting quality, and will leaven dough expofed to the air. At the time of the falling of this dew, the natrum pits grow full of that fait : and Vanflebius, Sands, and many others, join in affirming, that at this time the air becomes greatly more healthy; and tho' before the falling of this dew, or the inundation of the Nile, people die of the plague to the number of five hundred in a day in Grand Cairo, after this not one dies of that difeafe. It is eafily feen, that the overflowing of the Nile does not produce this' effect, but the dews and air, which at that time are full of that volatile alkali, which is one of the principles of thenatrum. People who have preferved fpecimens of the natrum have alfo ob- ferved, that they would grow much heavier on being expofed to the air at the time of the overflowing of the Nile. Phil. Tranf. N° 160.

NA-