with facility and precifion; and the more recent and fuccessful application of this valuable invention, to the measuring of the angular distances of the fun and moon, and of the latter from the fixed ftars, for the purpose of ascertaining the longitude; render every attempt to explain the nature of inftruments of this kind, and to improve them, particularly meritorious. Confidering the extreme flowness with which this valuable inftrument made its way in the nautical world, even in the plain and eafy cafe of finding the latitude by its means; it may not be amifs to quote what fo excellent and experienced a judge as Captain Cook has very lately faid in its favour, in the evidently more difficult and complicated task of determining the longitude: as fuch a teftimony cannot fail to promote its more ready and extenfive adoption among our maritime brethren, for this important purpofe; and to leffen their fears with refpect to the difficulty of the operations. After a full and fair trial of this inftrument, through long and complicated courfes, in an unknown fea, this experienced obferver declares that the method of finding the longitude with it at fea, is the most eafy, and attended with the leaft expence to the obferver. Every fhip,' he adds, that goes to foreign parts may be fupplied with a fufficient number of quadrants at a fmall expence; I mean good ones, proper for making, these obfervations For the difference of the price between a good and bad one, I apprehend, can never be an object with an officer. The most expenfive article, and what is in fome measure neceffary, in order to arrive at the utmoft accuracy, is a good watch; but for common ufe, and where that ftrict accuracy is not required, this may be difpenfed with.' In a preceding part of his journal he obferves that the greateft error this method of obferving the longitude at fea is liable to, does not exceed a degree and a half, and in general will be found to be much lefs. Such is the improvement navigation has received by the aftronomers and mathematical inftrument makers of this age: by the former, by the valuable tables they have communicated to the public, under the direction of the board of longitude, and contained in the aftronomical Ephemeris; and by the latter, from the great accuracy they obferve in making inftruments, without which the tables would, in a great mea fure, lose their effect.' He obviates the objection which may be made to this method of difcovering the longitude, on account of the fuppofed difficulty of the procefs, by obferving that any man, with proper application, and a little practice, may foon learn to make these obfervations as well as the astronomers themselves. I have feldom,' he adds, 'known any material difference between the obfervations servations made by Mr. Wales, and those made by the officers at the fame time *. Thefe difficulties are very confiderably leffened by the performance now before us; the principal part of which is a kind of elementary treatife, in which the author explains, in the most minute and perfpicuous manner, the conftruction of these inftruments in general; and defcribes every effential member of which they confift: with a view that the obferver may acquire the advantage of being thoroughly acquainted with the conftruction and powers of his inftrument. He next gives the most minute and accurate directions with regard to the preliminary and effential operation of rectifying all the feveral parts of which the inftrument confifts; and points out all the circumstances neceffary to be attended to, previous to, and during the obfervation. He next treats in detail of the corrections receffary to be made, in obfervations for taking the latitude; and illuftrates his rules by a variety of plain and inftructive examples, in which thefe corrections, whether neceffary or contingent, are introduced. The method of using these quadrants for the difcovery of the longitude, by the lunar obfervations, is explained with the fame perfpicuity and accuracy, and is likewife illuftrated with examples. The author next treats of the various applications of these inftruments to aftronomical obfervations, furveying, and other operations on fhore; by employing an artificial horizon, of water, treacle, mercury, or looking glafs. To these various ufes of this valuable inftrument we may add that to which it was lately, we believe, for the first time, applied, by Mr. Wales, in the island of New Caledonia, in measuring the quantity eclipsed, in an eclipfe of the fun; in which operation, according to Captain Cook's opinion, it answers the purpofe of a micrometer, to a great degree of certainty. In this didactic part of Mr. Magellan's treatife, he does not content himself with barely laying down a fet of authoritative rules or precepts for obferving; but every where gives the principles on which they are founded; fo that the most ordinary obferver cannot fail to comprehend the rationale of each operation. His obfervations are not however confined to the mere tyro; as this treatife contains many new and useful remarks, hints, &c. which are worthy the attention of the most practised obferver. In the remaining part of this performance the author describes a New double Sextant, invented by himself, which appears to poffels several peculiar advantages. Among others we fhall only mention that, from the very nature and conftruction of the in *See Cook's Voyage, vol. 1. pag. 40, and vol. 2. p. 101,102, & alibi. strument, ftrument, and the manner of using it, the obferver is fecured, from a variety of errors which may arife either from the original imperfection, or cafual derangement of the inftrument, or from other fources of error, which may operate at the time of obfervation. Angles likewise may be measured with it greatly exceeding the value of the limb.-But for the description of this inftrument, and its ufes, and for the many other particulars contained in this treatise, we must refer to the work itfelf; in the perufal and study of which the marine obferver will find the author to be an ingenious, fure, and useful guide. IT ART. XIX. By. Hiftoire et Memoires, &c.-The Hiftory and Memoirs of the Society formed at Amfterdam, for the Recovery of Perfons apparently drowned. Tom. II. Part 2. 8vo. Amfterdam. Meijer. 1776. T gives us pleasure to record the continued fucceffes of this beneficent Society, the parent of many others inftituted in different parts of Europe, for the fame humane and laudable purposes. The prefent hiftory of their tranfactions is preceded by accounts of other fimilar inftitutions, formed on their general plan; particularly of that which was established in our yown metropolis, in 1774. This fecond part of their fecond volume contains 58 new cafes of refurrections, in which the honorary medal, or the pecuniary premium, has been difpenfed by the Society, fince their laft publication. CORRESPONDENCE. B....y. WE have been defired, and readily comply with the request, to publifh the following prize questions, in mathematics, phyfics, and history, propofed for the year 1777, by the Society of Sciences at Copenhagen. The differtations on thefe fubjects must be written either in the Latin, French, Danish, or German tongues: and the reputed beft effays on each of thefe fubjects will intitle each of their refpective Authors to a gold medal of one hundred Danish crowns value. In MATHEMATICS. • As feveral methods bave been propofed, in our times, of meafuring moderate diflances, at one station, by means of one or two telescopes: the best and most commodious difpofition of fuch inftruments, for this purpose, is required; and likewife the degree of precision which may be expected from them.' In PHYSICS. To determine, by actual experiments, whether the fixed vegetable alcali be a fimple falt, or compounded of other fubftances. Without forming any pretenfions to the proposed prize, for the folution of this queftion, we fhall take upon us to determine it, gratis, in three lines; by obferving that the fixed 6 vegetable Vegetable alcali is not a fimple falt; as it is undoubtedly a com? bination confifting of alcali and mephitic acid, or the acid of fixed air; to which laft principle it owes a very confiderable part of its weight, or fubftance, and many other of its properties. Whether the purely alcaline part of this femi-neutral and compound fubftance, or, in other words, the caustic alcali, be fimple or compound, is a queftion which we cannot inveftigate in this place. In HISTORY. To determine the time when the government of the Danes commenced in Efthonia; what increase and change it underwent from the time of Valdemar II. to that of Valdemar III. when it wholly ceafed; what where the political and religious conftitutions of this country under their government; and what remains are yet to be found there of the Danish laws.' The candidates are required to obferve the ufual forms, relative to fecrefy, &c. prefcribed in these cafes; and to forward their differtations, free of poftage, before the 31ft of Auguft, 1778, to his Excellency M. de Hielmftierne, Privy Counsellor to his Danish Majefty, Knight of Dannebrog, and Prefident of the Society. B....y. Our fenfible and candid correfpondent F. V. has been deceived as to the meaning of the Italian philofopher, who (in the paffage quoted) did not intend to affirm that a certain degree of heat deftroys the animalcules and prevents their production ; for his conclufion (from no animalcules being produced from the infufed fubftances in his experiment with veffels hermetically clofed and plated in boiling water) was not, that the heat had deftroyed thofe animalcules, but that there were in the infufed fubftances no specific germs, the only generative principles from whence, according to the Abbot's hypothesis, animalcules can be produced. This is explained fully in the Abbot's effay referred to in the extract. The experiment made on infufed vegetables, in veffels hermetically clofed, was not defigned to try the force of the fire upon the germs, but to hinder thefe fpermatic getms from entering into the veffels, and thus to fhew, that, without them, no animalcules could be produced. And therefore in this, as well as in the other paffage, the Abbot supposes that no degree of heat would hinder the production of the animalcules, if the germs were really in the veflels, as no infufion of vegetables would produce them, if the germs were not there. M.... See Monthly Review, Vol. liv. June 1776. p. 430, &c. 7 FOREIGN LITERATURE. FRANCE.. ART. I. INCE, in fpite of all the dictates of reafon, and all the feelings of humanity, commercial avarice perpetuates the flavery and degradation of an unhappy part of mankind, the following work deferves the attention of all who are concerned in this merciless traffic: Traité fur le Gouvernement des Efclaves, i. e. A Treatise concerning the Method of governing Slaves. By M. PETIT, Deputy of the Supreme Council established for the Direction of the Colonies. 8vo. 2 vols. Paris. 1777. The labours of this connoiffeur in the fcience of flave-oeconomy, have not been confined to the formation of a code of French, English, and Spanish laws relative to the government of flaves in the Colonies of these three nations: he has extended his views farther, and draw an interefting parallel between thefe laws. In this parallel the Reader will perceive, immediately, the advantages that one nation has above another, in this respect; also the changes and improvements that may be made in this species or branch of legislation. M. PETIT obferves, that in 1771, the flaves of the French American Colonies amounted to 386,500, reckoning 240,000 at St. Domingo, 75,000 at Martinico, 64,000 at Guadaloupe, 4000 at St. Lucia, and 3500 at Cayenne; to fupply the annual deficiency in which number, an annual importation of 20,000 Blacks is neceffary. This renders the improvement of a legiflation, in which fo great a number of individuals is concerned, an object of confequence; and it must be confeffed, that the views opened by M. Petit, relative to this matter, difcover not only penetration, knowledge and capacity, but even humanity, and a liberal turn of mind. II. Hiftoire Veritable des tems fabuleux-i. e. A true History of the fabulous Ages; a Work, which, by unfolding the TRUTH which fabulous History had altered or disfigured, is defigned to throw Light upon the Origin and Antiquities of the earliest Nations, and more especially to vindicate facred Hilary. By M. GUERIN DU. ROCHER, 8vo. vols. i. ii. and iii. Paris. 1777. Here we have another of thofe learned and fanciful feekers, who love to grope in the dark, and form large hiftorical volumes from feanty materials, and dubious records. It is here that faith derives a great part of its fubfiftence from fancy, and (what is ftill more mortifying) is as barren in its fruits as it is uncertain in APP. Rev. Vol. lvi. its & |