158 KANSAS UNIVERSITY QUARTERLY. 
length of each radius vector and measure it off by use of the deci- 
mal scale, estimating tenths of tenths on the scale, thus setting off 
results to hundredths. And this is entirely satisfactory in the re- 
sults attained, but it is found tedious figuring each radius and 
measuring it off. A diagram from which each radius line can be 
set off at once by the dividers is desirable. Then a few of the 
radii may be measured as a check on the graphical work. 
Hence the following has been devised as by far the best drawing 
board construction for this spiral. It obviates all the difficulties of 
of the preceeding and is very satisfactory in all respects. 
PRACTICAL DRAWING BOARD CONSTRUCTION FOR THE 
SPIRAL. 
Lay out the diagram of Fig. 4, drawing first the two lines OY 
and OX at right angles. Then choose the distance OM, as large 
as the size of the paper will permit, allowing room at the right of 
M, for at least % OM. OM isto represent the degrees of one cir- 
cumference, 360. Then draw AH parallel to OM at a distance 
: Cite 
above, equal to the constant c, of the equation er agin the same 
scale as the 360. That is, if we choose 120 for the value of the 
constant c, and this gives a very satisfactory size of the spiral, c 
: 120.) wer 
will be made 560 ea of the length chosen for OM. Having drawn 
AH, draw AD at unit’s distance to the right of OY to the same 
scale which is to be used for r on the plotting. If ris to be meas- 
ured in inches, as is usually the case, make AD one inch to the 
right of OY. 
