132 MEMOIR OF C. F. BEAUTEMPS-BEAUPEE. 



positions of all the rcmarkaLlo objects of the coasts of France which can be 

 seen from the soa ; and it was by hearings directed upon these points, rigor- 

 ously determined, that M. Beautemps-Bcanprc; and his assistants iixed the posi- 

 tions of the points of the sea wliich were to be marked on the charts and plaus. 

 The bearings were invariably taken with the reflecting circle, in the managTi- 

 mcut of wliich valuable and delicate instrument M. lieautemps-Beauprc had 

 acquired great dexterity. Nor was he less expert in constructing graphically on 

 the lirst rough draught of his chart the points observed by his method, founded 

 on the geometrical principle of the " problem of three points." lie was 

 master in a surprising degree of the varied constructions deducible from this 

 principle, and applied them, as the case might require, with the utmost readi- 

 ness and sagacity. 



It is usually by means of the circumferences of circles described with the ob- 

 served distances that the points of station are obtained; but when this construc- 

 tion presents some difficulty by reason of the length of the radius of the circle, 

 the nearness of centres, &c., it is practicable to substitute one of those somewhat 

 numerous and generally quite simple constructions which elementary geometry 

 deduces from the same fundamental theorem. Tlius, in many circumstances, 

 calculation may be used to find the radii and centres of the circles to be described. 

 M. Beautemps-Bcauprii recommends for these constructions, combined with 

 calculation, the employment of the tables of natural tangents and sines. 



The scale adopted by the hydrographic engineers for the first reduction of 

 the • labors Avas six lines for 100 toises, or YiToo' equal to six times that of the 

 cb of Cassini. The charts, aiid even plans, however, have been generally 

 published on a scale much smaller, but M. Beautemps-Beaupre soon recognized 

 the propriety of not only collecting the materials requisite for the execution of 

 the new charts of the coasts of France, but of exerting himself, moreover, to 

 bring together in the archives of the depot of marine all the documents which 

 might be useful in the sequel for forming a judgment of any projects relating 

 to navigation. He suffered himself to be deterred neither by the difficulties nor 

 magnitude of the work, and the depot found itself eventually in possession of a 

 collection of five hundred and twenty-seven quarto volumes, containing the 

 documents requisite to execute at need, on the largest scale, the plan of all parts 

 of the western and northern coasts of France to which the- attention of govern- 

 ment might be called. 



One of the most essential and useful parts of marine charts is the indication of 

 the depths of the sea at difterent points obtained by the sounding line and denoted 

 by figures on the chart. M. Beautemps-Beauprd was equally skilled in making 

 and in marking the positions of soundings, and it is with the authority of a 

 practised master that he recapitulates in the Expose des Travaux, Sfc., the rules 

 of the difficult art of submarine topography. It was seldom that an obstruction 

 or peril escaped him, though he seems to take pleasure in citing, for the instruc- 

 tion of his successors, instances in Avhich his researches were baffled for years 

 in succession. One day notice was given him that a vessel had touched upon 

 a rock at a point where none was known to exist. He sought for it a long time 

 without success, but at last his line fell upon it. The rock was siniply a peak 

 whose diam(!ter scarcely exceeded that of the lead of the sounding line. 



It is necessary to take accoiuit in soundings of the constant variations of the 

 level of the sea by reason of the tides. " The first thing to be done," says our 

 hydrographer, "at the commencement of a campaign, on a coast where the water 

 througli this cause continually changes its level, is to place a certain number of 

 scales, divided into feet and inches, on which those changes shall be observed, 

 since it is by means of observations of this kind that we are enabled, in giving 

 the chart its definite form, to reduce to the lowest water' level the soundings 

 made at all hours of the day and tide. To reduce the soundings is to subtract 

 from the depths found on different days and at all hours of the tide, for every 



