POL
POL
by polijhhig in tins manner are To great, that the fiiell is often not to be known afterwards for the fame it was ; and hence we hear of new fliells in the cabinets of collectors, which have no real exiftcnce as fcparate fpecies, but are the policed appearance of others well known. To caution the reader againft errors of this kind, it may be proper to add the moft remarkable fpecies thus ufually altered. The onyx-fhell, which in its natural flare is of a fimple pale brown, when it is wrought fligbtly, or pdifljed with juft the fuperficies taken off, is of a fine bright yellow ; and when it is-cat away deeper, it appears of a fine milk-white with the lower part bluifh : it is in this ftate that it is called the onyx-fhell; and it is preferved in many cabinets in its rough irate, and in its yellow appearance as different fpecies of fliells. The violet fhell, fo common among the curious, is a fpecies of porcelane, which does not appear in that elegance till it has been polijhed ; and the common auris marina fhews itfelf in two or three different forms, as it is more or lefs deeply wrought. In its rough ftate it isdufky and coarfe, of a pale brown on the outfide and pearly within ; when it is eaten down a little way below the furface, it fhews variegations of black and green, and when ftill farther eroded it appears of a fine pearly hue within and without.
The nautilus, when it is polijhed down, appears all over of a fine pearly colour, but when it is eaten away but to afmall depth, it appears of a fine yellowifh colour with dufky hairs. The burgau, when entirely cleared of its coat, is of the moft beautiful pearl-colour; but when only flightly eroded, 3t appears of a variegated mixture of green and red ; whence it has been called the parroquet-iheW. The common helmet- fhei!, when wrought, is of the colour of the fined agate; and the mufcles in general, tho' very plain fhells, in their common appearance, become very beautiful when polijhed, and (hew large veins of the moft elegant colours. 7'he Per- fian {hell, in its natural ftate, is all over white, and covered with tubercles; but when it has been ground down on a wheel, and folijhed, it appears of a grey colour with fpots and veins of a very bright and highly fo&jhed white. The lim- pets in general become very different when polijhed, moft of them fhewing very elegant colours ; among thefe the tortoife- fhell-limpet is the principal ; it does not appear at all of that colour or tranfparence till it has been wrought. That elegant fpecies of fhell called the junquil-chama, which has deceived fo many judges of thefe things into an opinion of its being a new fpecies, is only a white chama with a re- ticulated furface ; but when this is polijhed, it Iofes at once its reticular work and its colour, and becomes perfectly fmooth and of a fine bright yellow : and the violet-coloured chama of New England, when worked down and polijhed, is of a fine milk-white with a great number of blue veins difpofed like the variegations in agates.
The afle's ear-fhell, when polijhed, after working it down with the file, becomes extremely glofly, and obtains a fine rofe-co- lour all about the mouth. Thefe are fome of the moft fre- quent among an endlefs variety of changes wrought on fhells \>ypolijhing ; and we find there are many of the very greateft beauties of this part of the creation which muft have been loft but for this method of fearching deep in the fubftance of the {hell for them.
The Dutch are very fond of fhells, and are very nice in their manner of working them : they are under no reftraint, how- ever, in their works, but ufe the moft violent methods, fo as often to deftroy all the beauty of the fhell. They file them down on all fides, and often take them to the wheel when it muft deftroy the very characters of the fpecies ; nor do they flop at this, but determined to have beauty at any rate, they are for improving upon nature, and frequently add fome lines and colours with a pencil, afterwards covering them with a fine coat of varnifli ; fo that they feem the natural lineations of the fhell : the Dutch cabinets are by this means made very beautiful, but they are by no means to be regarded as inftruaors in natural hiftory. There are fome artificers of this nation who have a way of colouring fhells all over with a different tinge from that which nature gives them; and the curious are often deceived by thefe tricks into the purchasing them as new fpecies.
There is another kind of work beftowed on certain fpecies of fhells, particularly the nautilus ; this is the engraving on it lines and circles, and figures of ftar?, and other things : this is too obvious a work of art to fuffer any one to fuppofe it natural. Bonani has figured fcvcral of thefe wrought fhells at the end of his work, but it is miferably throwing away labour to do them ; the fhells are fpoiled as objeas°of na- tural hiftory by it, and the engraving is feldom worth any thing. They are principally done in the Eaft-Indies. Shells are fubjedt to feveral imperfedions ; fome of thefe are natural, and others accidental : the natural ones are the effect of age, or ficknefs in the fifh. The greateft mifchief hap- pens to fhells by the fifh dying in them. The curious in thefe things pretend to be always able to diftinguifh a fhell taken up with the fifh alive, from one found on the fhores : they call the firft a living, the fecond a dead fhell, and fay that the colours are always much the fainteft in the dead fhells.
When the fliells have Iain long dead on the fhores, they are fubjedt to many injuries, of which the being eaten by fea- worms is not the leaft : age renders the fineft fhells livid or dead in their colours.
The fineft fhells arc thofe which are fifhed up at fea, not found on the fhores. The other natural defects of fhells are there having morbid cavities, or protuberances, in parts where there fhould be none. When the fhell is valuable thefe faults may be hid, and much added to the beauty of the fpecimen, without at all injuring it as an object of natural hiftory, which fhould always be the great end of collecting thefe things. The cavities may be filled up with maftic, diflblved in fpirit of wine, or with ifinglafs ; thefe fubftances muft be either co- loured to the tinge of the fhell, or elfe a pencil dipped in wa- ter colours muft finifh them up to the refemblance of the reft, and then the whole fhell being rubbed over with gum-water, or with the white of an egg, fcarce any eye can perceive the artifice ; the fame fubftances may alfo be ufed to repair the battered edge of a fhell, provided the pieces chipped oft" be not too large. And when the excrefccnces of a fhell are faulty, they are to be taken down with a fine file. If the lip of a fhell be fo battered that it will not admit of repairing by any cement, the whole muft be filed down to an evennefs, or ground on the wheel. POLITICAL (Cycl.)— Political arithmetic. According to Mr. Kerfcboom's computation, the inhabitants of Holland and Weftfriezeland, in the year 1738, amounted to 980000.- He has given us a table of the particulars, exhibiting the number of people of all ages, living at the fame time, from their birth to extreme old age. This table having the chan- ces of mortality within the ages mentioned, he calls the table of contingency of life and death.
This table is calculated upon three principles: r. On cor- rect obfervations upon the tables of affignable annuities in Hol- land, which have been kept there for above 125 years; wherer in the ages of the perfons dying are truly entered. 2. Upon a fuppofition that there are yearly born in the two provinces 28000 living children. 3. That the whole number of inha- bitants, in any country, is to thenumber of births as 35 to 1. From this table it appears, r. That more than half the num- ber of people in the two provinces are above 27 years old. 2. That by the obfervations made in England, out of 35 children born, 18 of them are boys, and 17 girls: the in- habitants of Holland and Weftfriezeland, confift of 504000 males, and 476000 females, the mm of which is 980000. Here follows the table of contingency of life and death. Of above 90 years old 500
Of 90 to 86 incl. 2500
85 81 6500
80 76 13000
75 71 20300
70 66 2 7300
65 6 1 34300
60 56 40800
55 5i 47 000
50 46 53000
45 4' 57800
40 36 62500
35 3- 1 67600
30 27 58400
491500 film above 27 years old.
Of 26
16
to birth
9+300 834.00 87200 91800 131800
488500 fum under 27 years old.
491500
488500
980000 fum of all the inhabitants.
Mr. Kerfeboom obferves from the affignable annuities for lives before- mentioned, that females, one with another, live about three or four years longer than the fame number of males. He alfo thinks there is no reafon to differ from the proportions affigned by Mr. King (in Davenant's effays) of the ftate and condition of the inhabitants of England ; which is, that for every 1 00000 inhabitants there is
Married men and women 34500
Widowers 1500
Widows 4500
Unmarried youth and children 45000
Servants , 1 0500
Travellers, ftrangers, fcfV. 4000
