in lairing out Grounds. 



463 



To form a Volute where the Border is narroxoer toxsoard the Centre^ 

 like the shell of a snail, {fig. 72.) 



Make a circle as 

 before, and, instead of 

 driving the pegs up- 

 right, let them form a 

 cone; or, instead of 

 pegs, use a large flower- 

 pot whelmed, and, if 

 necessary, a smaller 

 one whelmed over it. 

 Measure the radius of 

 your volute, and wind 

 that complement of 

 line round the cone in 

 such a manner as to 

 correspond with the 

 varying breadth of 

 your intended border, and commence making the figure at the 

 interior, by unwinding the line, and you will have^^. 72. 



To delineate the Volute 

 Jig. 73.— Wind the hne 

 around the cone in the 

 same manner as for^. 72., 

 only unwind it from the 

 other end. 



A new method of striking 

 out Circles^ and other Cur- 

 vilineal Figures hy means of 

 a Theodolite^ or isoith a com- 

 mon Cross Staff" and Measur- 

 ing Chain, applicable alike to 

 circumscribe the area of one 

 inch, and the demesne of 

 several square miles. 

 With a Cross-Staff {fig. 1 5.) andChain. — Suppose a, inj'^-. 74-., 

 a point in the intended arc : stick a peg there, and, with the 

 handle of the cross staff stuck through the handle of the chain, 

 set up the staff in b (another point in the intended arc) with 

 the base pointing to a. Then measure the distance from b to a 

 (say 50 links) ; and let an assistant be directed to put in a peg 

 in r, forming a right angle with the line 6 a, at a certain ratio 

 from b (say 5 links). Raise the cross staff (putting a peg in its 

 place), and plant it at c, 50 links from b, and forming the line 

 era; set off 5 links on the line c r at right angles with the 

 line c b, and so on, till you end where you began. 



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