Page:The American Cyclopædia (1879) Volume IV.djvu/773

COAST SURVEY 757 important naval demonstration was made upon the coast without the presence of some officer from the same service on the staff of the ad- miral commanding the fleet. The services thus rendered to the country during the war by the officers of the coast survey were of the utmost importance, and were thoroughly ap- preciated by the government. Added to this, the accurate charts of the coast and harbors which had been already made and published were of the greatest assistance to our vessels in their cruises up and down the coast. Worn down at length with the labors of a busy life, Prof. Bache died in 1867, and Prof. Ben- jamin Peirce was installed as superinten- dent Feb. 26, 1867. Since his accession Prof. Peirce has continued with vigor the system inaugurated by his predecessor, and has great- ly extended and enlarged the sphere of useful- ness of the coast survey. The great system of a national triangulation, which extends the geodetic work, heretofore confined to the sea- coast, across the whole continent, owes its ex- istence, and in a great measure its conception, to the present superintendent. This work, which is now (1873) in successful operation, oon templates the establishment of. a system of triangles connecting those already determined on the Atlantic with those on the Pacific coast. Thus in every state and territory geodetic points will be established and accurately de- termined ; and thus will be formed a base for a thorough topographical survey of the several states, which will equal if not surpass in beauty and accuracy the famous ordnance survey of Great Britain, while in point of magnitude and extent it will surpass anything in the world. Prof. Peirce, on assuming charge of the survey, encountered some difficulties in the way of a vigorous prosecution of the work. As before mentioned, several of the vessels belonging to the survey had been captured during the war ; others were very old, and many were completely worn out and unfit for service ; and the small number remaining were totally inadequate for such activity in the field as had always heretofore existed. But these difficulties are rapidly being overcome. Prof. Peirce has urged upon congress the passage of special appropriations for the building of new vessels, and several fine ones have already been built and are at work upon their stations. The survey of the Pacific coast, which had been somewhat disorganized owing to the war, he established upon a new and firm basis, with an experienced officer at its head ; and the work upon that coast has proceeded with un- exampled rapidity. Much valuable scientific information has been obtained by the observa- tions of the solar eclipses made by the super- intendent and his assistants, under special acts of congress, in 1869 and 1870. Much has been done, and very valuable information collected, through the observations for deep-sea temper- atures ; and the many thousand specimens col- lected from the bottom of the sea at great depths have added much to our knowledge of the character of the great sea floor. The inves- i tigations which have been made of the tides I are of great importance ; they will be referred , to in their proper place. A directory or coast pilot of the Pacific coast has been published for the use of mariners, and one is in prepara- tion for the Atlantic and gulf coasts. Every year increases the general usefulness of the survey and the vigor and success of its prose- cution. These general facts with regard to the history and progress of the United States coast survey being stated, we come to the scientific and practical operations involved in its execution. An explanation of these opera- tions will embrace a variety of topics, and only a brief notice of each can be given. The first object of a work of this kind is an accurate determination of the shore line. This is done entirely by operations upon land. The object of a map or chart is, of course, to give a mini- ature representation of a portion of the earth's surface upon paper, in such a manner that the different parts of the drawing shall have the same relative positions and dimensions as are found in nature. To determine these dimen- sions by linear measurement, for the purpose of reducing them to the scale of the drawing, would be practically impossible ; and hence the use of geodetic or trigonometrical surveying. Geodesy General RemarTcs. To illustrate this mode of measuring distances and estab- lishing the relative positions of points on the earth's surface, let us suppose ourselves to be on a level plain, surrounded in the distance by high mountains, and that we wish to determine the distances from our position to the tops of those mountains, and of the different moun- tain peaks from each other. A line is mea- sured on the plain, of such a length that if two lines be drawn from its extremities to one of the mountain tops, they will intersect at a considerable angle, and form with the mea- sured line a triangle of proper dimensions. Then, knowing the length of one side of this triangle, we may compute the length of the other two sides by a simple theorem of trigo- nometry, without any further labor than mea- suring the angles of the triangle. Taking now either of the computed sides as a new base, we may establish a second triangle upon this, and thus fix the position of another point. A third point may be established in the same manner, gradually expanding the system until the whole region we wish to embrace in the map is covered with a network of triangles ; the length of the lines having been computed by measuring the first only, and then mea- suring the angles of the triangles. For the purpose of a map or chart, there are still two important elements wanting. We have yet no means of knowing the direction of any one of these lines with reference to the meridian, nor the place which the points occupy on the surface of the earth. The survey thus far will give no means of knowing whether