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Have been hinted at in. different parts of this tract, tvbich,with others, are here collected together, that they may readilybe seen in one point of view: They are principally these*

Procure one base, or more if convenient, very accuratelymeasured, ih such situation, that as many tiiote points aspossible in the survey may be seed from it. Assume as manyprincipal ®r eminent points and objects aS may be propel"and convenient; and fi"om each one of them, measure theangles formed by all the rest that can bfe seen, both horizontaland vertical angles; arid repeat these observations, if conve-nient, with the instrument varied or reversed, taking themeitris among the several quantities of each angle. Takethen as many sections of the ground, and as far extended iriall directions, as the time and circumstances will possiblyadmit. Of the sections^ those that are horizontal, or level,ate the best, as they require no calculation; procure there-fore as many as possible of them. In vertical sections, ob-serve the vertical angles, not in the plane of the section, butat some other point of which the bearing is also taken fromtile beginning of the section line, and w'here thfe horizontalangles of the poles are taken, for the reasons before mentionedin p. 22. And it will be a still further convenience if thesection be made in such direction^ as to form a right anglewith the line drawn to the point, or station, from which thevertical angles of the poles are observed, as may be seen fromwhat is said in p". 21. It might perhaps be proper to makesome experiments on a valley, instead of a hill, taking twoObservatories at the two opposite sides of it, both for thegreatef variety in this interesting problem^ and because alsothe survey wduld be more easily made, on account of theground being more 1 in view at each station, than in the caseof a hill, which generally hides mote than half the compassfrom the observer. In computing the relative altitudes ofall the principal stationsj let the operations be performedmutually both backward and forward, that is, from both ofevery two objects, having for that purpose observed at each•f them the vertical angle Of the other, namely, both the

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