XIII, C, 4 
Shaw: Microtechnical Methods 
257 
The slide rule was found most satisfactory for making the 
calculations. It is operated as follows : find n on scale A ; bring 
c, the constant 9 2578, on scale B opposite n; set the hair line 
of the runner at d on scale C; the number, N, is thereby 
marked by the hair line on scale A. The position of the decimal 
<ev — 
7 
* , 
< 
kTq 
} ' 
0 0 
^ 0 
°°o' f 
3 ~o 
0° 
r% 
r 
0 q: 
0 0 
V/ 
O O 
■O ^ 
0 v 
0 
— 
.0 c 
'#0 
“57 
b O 
> 
to 
5 < 
U~Ol 
>°'a 
o3 
io O 
Q, 
jo"®* 
;:p*9 
-O P i 
' 0 .- 
' OV P 
TXT- 
0 6 
■> r\ : 
> *•'» 
Op**. 
4 
-AJ A 
O'o 
,Oc 
pro 
■O 0 
o ' 
: 0 1 
O 0)1 
• 0 4 
0-0 ( 
•O o' 
) O c> H 
oo'- 
< 
3 0 
0 c 
>: 0 Z 
ClQ. 
\J* W 
>/ ° < 
.0 0 
;o c 
► :° O 
:n 
+? = ui 
7 
■ 3 
; z 
’ / 

• 
Fig. 5. A sketch of cells of a coenobium included within an area of 8,100 sq. p indicated 
by the portion of the square-ruled ocular micrometer sketched at the same time. In practice 
the grouping lines, here drawn dotted, are drawn in red ink. The upper right square was 
not used because of some interfexing object, the appended square at the right being subs- 
tituted for it. 
point in the number may be quickly found by reference to a 
previously prepared table of counts and diameters corresponding 
to cell numbers 1,000 and 10,000. Such a table may be easily 
made from slide rule readings. 
The foregoing may be illustrated by the following example : A 
spheroidal coenobium is found to have transverse and polar dia- 
meters of 610 and 635 p. respectively measured from center to 
9 For convenience in operating the slide rule I have marked this constant 
in two places on the slide rule which I use. To accomplish this in the 
best way, set the 8.1 mark on scale B under the ^ mark on scale A. Then 
make a mark on the B scale under the 1 mark of scale A. Then set the 81 
mark on scale B under the it mark on scale A, and make another mark 
on scale B under the 1 mark on scale A. I cut these marks in the celluloid 
with a suitable sharp knife and fill them with red paint. This instrumental 
constant, dependent on the area selected for the counting of cells, is not 
to be confused with the constants c and c 1 which are marked on the C 
scale of some slide rules to indicate the square roots respectively, of four 
and forty times the reciprocal of v. 
