an Insirument called The Sectograph. 403 
ten divisions; then with the first finger of the right hand 
make a dot ‘with the 7th point, (which may easily be done 
without marking with the other points,) which distance 
will be one-hundredth of an inch; then raise the 7th point, 
move to another division, dot, &c.&c. By using every 
second division you will have the fiftieth of an inch, &c. 
Fractional parts of distance may be measured by the same 
means, 
The Sectograph and Scale for dividing Circles, Angles, Lines, 
Se 
This sectograph is exactly the same as the former, except 
that of its not having the graduated scale e, g; instead of 
which it is accompanied by a scale, the size of the in- 
strument when opened to its greatest extent, that is, about 
eight inches and a half Jong and five-eighths of an inch 
wide, Both being of the same dimensions, are neatly 
packed in one case. 
The ivory scale has on one side a diagonal scale of inches ; 
on the other, polygons, sines, tangents, semi-tangents, and 
chords ;—the whole constructed expressly for the instru~ 
ment. 
The Use of the Sectograph and Scale. : 
The first (0) and last point (8) on the line of points are 
called the extremes ; the single point (at A or B) the cen- 
tral point. 
To divide any line, AB, fig. 1. into a given number of 
equal parts, each less than the greatest, but greater than 
the smallest division that can be made by the instrument. 
Rule. 
1. Draw AC (fig. 1.) making any angle with AB. 
2. Take any distance as Ai between the extreme points, 
and repeat it as often as necessary along AC; as from A 
to 1,1 to 2,2 to 3, &c. 
3. Press down the points in the last division, as from 3 
to 4, and let C be the required point. 
4. With the same extent of the sectograph and one ex- 
treme in C, let the other fall in D. 
5. Join CB, and parallel thereto draw DE; then BE is 
one extent of the sectograph on the line AB, to which 
apply it and finish the division. 
Example. Let it be required to divide the line AB into 
twenty-nine equal parts with an instrument of eight divi- 
gions, or nine points, 
Ceca Proceed, 
