i

1802.]

Should the land be exceedingly flat, the draining will then re- quire a great degree of ſkill to execute, as the ſpirit-level muſt be abſolutely uſed to work with proper diſpatch and efe; and as very few but profeſſed ſurveyors thoroughly underſtand its uſes, it may not perhaps be inapplicable, for the ſake of thoſe pradtical farmers who are unacgquainted with them, to ſay a few words on the ſubje(Æ.|;

One of the purpoſes for which the level is particularly uſeful, is that of ſetting out ſtraight lines; which is eaſily done in the following manner, by the vertical hair in the teleſcope, to the greateſt nicety, no matter how great the length required may be,

er

Y Z e e

wR a TZ 72/ L. 4B as ur rt

NE Mp

———————————

A the level; B a ftaff fixed at the extremity of the drain in- tended to be cut from A to B. It is evident, if the teleſcope at A be pointed towards the ftaffat B,(it is of no conſequence whe- ther the level be ſet truly parallel to the earth or not,) and’ pins be put down in ſuch a manner as to be intercepted by the ver- tical hair, they muſt form the ſtraight line A B,

There is one other purpoſe for which it is ſtill more uſeful, that of aſcertaining at any given point the exact depth any drain ought to be according to the fall of the whole.

E CS =(rb Su s

e M E i OE fa

A. the level; B’“ 2 ſaŒÆ ereded at the intended end of the drain; C the mark of the real level, or point of interſeRion of the hairs; D another mark, as many inches below C, as it is in- tended to have fall in the Drain. If the level be. lowered, ſo that the point of interſection, inſtead of being at C, be ac D, the line Com:& Ag. Mag. Val. FPI. H ù

On Draining. 417