their longitude by one degree.

But from the fatigue of continually observing the stars at night, in a cold thin air, joined to a weakly constitution, he was reduced to a bad state of health; for the recovery of which he desired leave to retire to his house at Horton; where, as soon as he found himself on the recovery, he began to fit up an observatory of his own, having first made an elegant and curious engine for turning all kinds of work in wood or brass, with a maundril for turning irregular figures, as ovals, crosses, wreathed pillars, &c. Beside these, he made himself most of the tools used by joiners, clock-makers, opticians, mathematical instrument-makers, &c. The limbs, or arcs, of his large equatorial instrument, sextant, quadrant, &c. he graduated with the nicest accuracy, by diagonal divisions into degrees and minutes. The telescopes he made use of were all of his own making, and the lenses ground, figured, and adjusted with his own hands.

It was at this time that he assisted Mr. Flamsteed in calculating most of the tables in the second volume of his "Historia Colestis," as appears by their letters, to be seen in the hands of Mr. Sharp's friends at Horton. Likewise the curious drawings of the charts of all the constellations visible in our hemisphere, with the still more excellent drawings of the planispheres both of the northern and southern constellations. And though these drawings of the constellations were sent to be engraved at Amsterdam by a masterly hand, yet the originals far exceeded the engravings in point of beauty and elegance; these were published by Mr. Flamsteed, and both copies may be seen at Horton.

The mathematician meets with something extraordinary in Sharp's elaborate "Treatise of Geometry Improved," (in 4to. 1717, signed A. S. Philomath), 1st. by a large and accurate table of segments of circles, its construction, and various uses in the solution of several difficult problems, with compendions tables for finding a true proportional part, and their use in these or any other tables exemplified in making logarithms, or their natural numbers, to 60 places of figures, there being a table of them for all primes to 1100, true to 61 figures. 2d. His concise "Treatise of Polyedra,” or solid bodies of many bases, both the regular ones and others to which are added twelve new ones, with various methods of forming them,

cies, and in numbers: illustrated with a variety of copper-plates, neatly engraved by his own hands. Also the models of these polyedra he cut out in box-wood with amazing neatness and accuracy. Indeed few or none of the mathematical instrument-makers could exceed him in exactly graduating or neatly engraving any mathematical or astronomical instrument, as may be seen in the equatorial instrument above mentioned, or in his sextant, quadrants, and dials of various sorts; also in a curious armillary sphere, which, beside the common properties, has moveable circles, &c. for exhibiting and resolving all spherical triangles; also his double sector, with many other instruments, all contrived, graduated, and finished, by himself. In short, he possessed at once a remarkably clear head for contriving, and an extraordinary hand for executing any thing, not only in mechanics, but likewise in drawing, writing, and making the most exact and beautiful schemes or figures, in all his calculations and geometrical constructions.

The quadrature of the circle was under. taken by him for his own private amuse. ment in the year 1699, deduced from two different series, by which the truth of it was proved to 72 places of figures; as may be seen in the introduction to Sherwin's table of logarithms; that is, if the diameter of the circle be 1, the circumference will be found equal to 3,141592653589793238 462643383279502884197169399375105820 974944592307816405, &c. In the same book of Sherwin's may, also be seen his ingenious improvements on the making of logarithms, and the constructing of the na tural sines, tangents, and secants.

He also calculated the natural and logarithmic sines, tangents, and secants, to every second in the first minute of the quadrant: the laborious investigation of which may probably be seen in the archives of the Royal Society, as they were presented to Mr. Patrick Murdock for that purpose; exhibiting his very neat and accurate manner of writing and arranging his figures, not to be equalled perhaps by the best penman now living.

The late ingenious Mr. Smeaton says, (Philosophical Transactions, anno 1786, p. 5, &c.): "In the year 1689, Mr. Flamsteed completed his mural arc at Greenwich; and, in the Prolegomena to his Historia Cœlestis, he makes an ample acknow.

ledgment of the particular assistance, care, and industry of Mr. Abraham Sharp; whom, in the month of August 1688, he brought into the observatory as his amanuensis; and being, as Mr. Flamsteed tells us, not only a very skilful mathematician, ́ but exceedingly expert in mechanical operations, he was principally employed in the construction of the mural arc; which in the compass of fourteen months he finished, so greatly to the satisfaction of Mr. Flamsteed, that he speaks of him in the highest terms of praise.

"This celebrated instrument, of which he also gives the figure at the end of the Prolegomena, was of the radius of 6 feet, 74 inches; and, in like manner as the sextant was furnished both with screws and diagonal divisions, all which were made by the accurate hand of Mr. Sharp. But yet, whoever compares the different parts of the table for conversion of the revolutions, and parts of the screw belonging to the mural arc, into degrees, minutes, and seconds, with each other, at the same distance from the zenith on different sides; and with their halves, quarters, &c. will find as notable a disagreement of the screw-work from the hand divisions, as had appeared before in the work of Mr. Tompion: and hence we may conclude, that the method of Dr. Hook, being executed by two such masterly hands as Tompion and Sharp, and found defective, is in reality not to be depended upon in nice matters.

"From the account of Mr. Flamsteed it appears also, that Mr. Sharp obtained the zenith point of the instrument, or line of collimation by observation, of the zenith stars, with the face of the instrument on the east and on the west side of the wall; and that having made the index stronger (to prevent flexure) than that of the sextant, and thereby heavier, he contrived, by means of pulleys and balancing weights, to relieve the hand that was to move it from a great part of its gravity. Mr. Sharp continued in strict correspondence with Mr. Flamsteed as long as he lived, as appeared by letters of Mr. Flamsteed's, found after Mr. Sharp's death, many of which I have

seen.

"I have been the more particular in what relates to Mr. Sharp, in the business of constructing this mural arc, not only because we may suppose it the first good and valid instrument of the kind, but because I look upon Mr. Sharp to have been the first person that cut accurate and delicate divisions VOL. VI.

upon astronomical instruments, of which, independently of Mr. Flamsteed's testimony, there still remain considerable proofs; for, after leaving Mr. Flamsteed, and quitting the department above mentioned, he retired into Yorkshire, to the village of Little Horton, near Bradford, where he ended his days about the year 1743 (should be in 1742), and where I have seen not only a large and very fine collection of mechanical tools, the principal ones being made with his own hands, but also a great variety of scales and instruments made with them, both in wood and brass, the divisions of which were so exqui. site, as would not discredit the first artist of the present times; and I believe there is now remaining a quadrant, of four or five feet radius, framed of wood, but the limb covered with a brass plate, the subdivisions being done by diagonals, the lines of which are as finely cut as those upon the quadrants at Greenwich. The delicacy of Mr. Sharp's hand will indeed permanently appear from the copper-plate, in a quarto book, published in the year 1718, intituled

Geometry Improved, by A. Sharp, Philomath,' (or rather 1717, by A. S. Philomath) whereof not only the geometrical lines upon the plates, but the whole of the engraving of letters and figures were done by himself, as I was told by a person in the mathematical line, who very frequently attended Mr. Sharp in the latter part of his life. I therefore look upon Mr. Sharp as the first person that brought the affair of hand division to any degree of perfec tion."

Mr. Sharp kept up a correspondence by letters with most of the eminent mathematicians and astronomers of his time, as Mr. Flamsteed, Sir Isaac Newton, Dr. Halley, Dr. Wallis, Mr. Hodgson, Mr. Sherwin, &c. the answers to which letters are all written' upon the backs or empty spaces of the letters he received, in a short hand of his own contrivance. From a great variety of letters (of which a large chest-full remains with his friends); from these and many other well known facts it is evident that Mr. Sharp spared neither pains nor time to promote real science. Indeed, being one of the most accurate and indefatigable computers that ever existed, he was for many years the common resource for Mr. Flamsteed, Sir Jonas Moore, Dr. Halley, and others, in all sorts of trouble. some and delicate calculations.

Mr. Sharp continued all his life a bachelor, and spent his time as recluse as a ber G

mit. He was of a middle stature, but very thin, being of a weakly constitution; he was remarkably feeble the last three or four years before he died, which was on the eighteenth of July, 1742, in the ninety-first year of his age.

In his retirement at Little Horton, he employed four or five rooms or apartments in his house for different purposes, into which none of his family could possibly enter at any time without his permission. He was seldom visited by any persons, except two gentlemen of Bradford, the one a mathematician, and the other an ingenious apothecary: these were admitted when he chose to be seen by them, by the signal of rubbing a stone against a certain part of the outside wall of the house, He duly attended the dissenting chapel at Bradford, of which he was a member, every Sunday, at these times he took care to be provided with plenty of halfpence, which he very charitably suffered to be taken singly out of his hand, held behind him during his walk to the chapel, by a number of poor people who followed him, without his ever looking back, or asking a single question.

Mr. Sharp was very irregular as to his meals, and remarkably sparing in his diet, which he frequently took in the following manner: A little square hole, something like a window, made a communication between the room where he was usually employed in calculations, and another chamber or room in the house where a servant could enter; and before this hole he had con trived a sliding board: the servant always placed his victuals in this hole, without speaking or making the least noise, and when he had a little leisure he visited his cupboard to see what it afforded to satisfy his hunger or thirst. But it often happened that the breakfast, dinner, and supper have remained untouched by him when the servant has gone to remove what was left, so deeply engaged had he been in calculations. Cavities might easily be perceived in an old English oak table where he sat to write, by the frequent rubbing and wearing of his elbows. Gutta cavat lapidem, &c. By Mr. Sharp's epitaph it appears that he was related to Archbishop Sharp; and Mr. Sharp, the eminent surgeon, who some years since retired from business, is the nephew of our author. Another nephew was the father of Mr. Ramsden, the present celebrated instrument maker, who says that his grand uncle Abraham, our author, was some time, in his younger days, an excise

man, which occupation he quitted on com ing to a patrimonial estate of about two hundred pounds a year.

SHASTER, or SHASTRAM, a sacred book, containing the religion of the Banians; it consists of three tracts; the first of which contains their moral law; the second, the ceremonial; and the third, delivers the peculiar observances for each tribe of Indians.

SHAWIA, in botany, so named in memory of Thomas Shaw, D.D. a genus of the Syngenesia Polygamia Segregata class and order. Essential character: calyx imbricate, with five or six scales, three interior longer; corolla five-cleft; seed one, oblong. There is only one species, viz. S. paniculata, a native of New Zealand.

SHEADING, a term used in the Isle of Man for a riding, tything, or division of that isle; the whole being divided into six of these sheadings; in each of which there is a coroner or constable, who is appointed by the delivery of a rod at the tinewald court, or annual convention.

SHEATHING, in ship-building, a sort of casing or covering nailed all over the outside of a ship's bottom, to protect the planks from the pernicious effects of the worms. It has been customary many years past to sheath the ships of the Royal Navy, and those of the East India service with copper.

SHEAVE, or SHEEVE, in maritime af fairs, the wheel on which the rope works in a block; it is generally formed of lignumvitæ, sometimes of brass, and frequently compounded of both the interior part, or that which sustains the friction against the pin, being of brass, let into the exterior, which is of lignum-vitæ ; it is then denomi nated a sheave with a brass bush.

SHEAVE hole, is a channel cut in a mast, yard, or timber, in which to fix a sheave, and answering instead of a block.

SHEEP, in zoology, a well-known genus of quadrupeds, the horns of which are hollow, bent backward, twisted, and rugose; the fore-teeth are eight, and the hinder ones are narrower than the others; there are no canine, or dog-teeth. See Ovis.

SHEEP. Any person who shall feloniously drive away, or feloniously steal any sheep or lamb, or wilfully kill any sheep or lamb, with a felonious intent to steal the carcase, or any part thereof, or assist or aid in com. mitting any of the said offences, shall be guilty of felony, without benefit of clergy. 14 George II. c. 6. Any person who shall

being from their rarity purchased at very high prices.

The vast variety of forms which shells possess, not only renders arrangement more necessary, but at the same time occasions the formation of that arrangement the more difficult. Dissimilarity in size and colour, as well as in form, which occur in shells of the same species, at different ages, adds much to this difficulty. External characters, however, sufficiently marking specific differences, may almost always be discovered in shells, at every period of their existence; and various attempts have hence been made, to dispose them in such a methodical arrangement, as should place each of them in its proper place; and should thereby occa sion them to be more readily recollected.

Lister, Langins, and other early writers on testaceology, have proposed different methodical arrangements of shells, which, from their imperfections, have been in tirely laid aside, and do not therefore require to be here noticed. Indeed it appears to be unnecessary to go further back than to the arrangement of the celebrated Linnæus, which seems, in its turn, to be yield. ing to later systems, rendered more perfect by the constant accession of new and illus trative specimens, and the consequent increase of knowledge. But previous to considering the proper method of arrangement, and to examining into even the generic differences, it will be proper to ascertain the characters which belong to shells in general, and to determine the precise terms by which they can be best expressed.

The division into univalves, bivalves, and multivalves is so clearly pointed out by nature, that it must be adopted in every well methodized arrangement, and may therefore be safely admitted in these preliminary observations. Univalve shells are discoidal when the spiral is formed on a horizon tal line, so that a section, made in that line, would divide the shell into two nearly equal parts; fusiform when it bulges in the middle, and has the two extremities of nearly equal length; turbinated, when the belly of the shell is very large and tumid compared with the spire, which is given off from its centre; and turriculated when the turns of the spire, gradually increasing, form an elongated cone.

The parts of univalve shells are, the back, which is the external bulging part of the turn opposite to the opening; the belly, the tumid part of the last turn, forming the right or outer lip; that being termed the

left which is formed on the columella, and which Linnæus distinguished as the columellar ridge. The spire is formed on the su perior part of the shell, the turns of which are formed round the columella, or little central column, reaching from the opening of the shell to the summit of the spire. These convolutions are numbered by reckoning that as one, which reaches from the external to the inner lip, and in the same manner to the summit; the line by which they are united being termed a suture. The spire itself is either pointed, obtuse, truncated, flattened, concave, convex, straight, oblique, or pyramidal. Its turnings are coronated, (beset with spines or tubercles), beaded, carinated, or canaliculated. The suture is crenulated, double, projecting, or effaced. The shell is said to be perforated, when a small umbilical cavity exists in the columella at the base of the shell, in the axis round which the spire is revolved; and imperforate when there is here no cavity nor umbilicus. Besides being either umbilicated or not, the columella may be flattened, truncated, caudated, canaliculated, spiral, and plaited, as in the Volutes. The umbilicus also may be slit, canaliculated, consolidated, crenulated, or dentated: it may also have a superadded cullus. The opening varies much in different shells; and where it narrows it acquires the name of throat; it terminates in a canal. The lip is eared, digitated, alated, grooved, slit, or wrinkled; the form of the opening depending much on that of the lip; it hence becoming angular, round, semicircular, longitudinal, transverse, linear, gaping, compressed, or reversed. The openings of shells are sometimes closed by a shelly or cartilaginous plano-convex body,termed operculum, which is disposed between the two lips, and fitted to the form of the opening. The flat surface of this body is marked by a spiral line.

A bivalve shell has the two valves, which constitute it, connected at the basis, or inferior margin; opposite to which is the superior margin; the shell being supposed to be placed on the hinge, its margin is divided into the anterior and the posterior margin. The length of the shell is measured from the inferior to the superior margin, and the breadth from the anterior to the posterior margin. The belly is the most tumid part, and the beaks, the prominences over the hinge, are of a conoidal and spiral form. At the basis of the shell is the hinge, by which the valves are moved on each other; and in the anterior chink a