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 



5 o 



00 



O 



.Q,.q>o 

 Od 



o o 



o 



0: 



■O ° 

 



SL-Oi 



0/ 



* nol\°o 



o^ r o. 



f 30\r 



m 



o o 



1*0 £2 



: 0: 

 ■4 -^J— 



.PCD 

 OO 



II AJL+1&, 



+? = llf 



Fig. 5. A sketch of cells of a coenobium included within an area of 8,100 sq. « indicated 

 by the portion of the suuare-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 interfering 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 /* respectively measured from center to 



• 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 v 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 t 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 *. 



