262 CHAP. XXVII. SIMULTANEOUS VARIATION OF FACTORS 



higher. But through the long median range — that is, from 

 22 C. to 29 C. — the ratio between the two activities is 

 exactly 2-5; it is slightly lower than this below 22 C, 

 and higher after 29 C. 



The fact that the ultimate value is the product of the 

 partial effects is conclusively demonstrated by the various 

 possible combinations, about a hundred in number, in 

 the median range. The limitation of space compels me, 

 however, to give only three typical examples. 



Example 1. — Temperature-variation from 21° C. to 

 25° C 



The factor of light. — The activity under S is 2-5 times 

 that under • 4 S (through the range of 22 C. to 29 C.) . (1) 



With constant light at intensity 0-4 S, the partial effect 

 for temperature- variation is — - 



Activity at 25° = i3i-7.., Q , 2) 



Activity at 21 88-5 ^ ' K) 



Hence the activity for S at temperature 25 C. is— 



Calculated value, (1) X (2) X activity at 21 

 = 2-5X 1-49 x 88-5 = 329-7 c.mm. 

 Observed value = 328-0 ,, 



Example 2. — Temperature- variation from 23 to 27 . 

 Light changed from 0-4 S to S. 



Partial factor for temperature-variation at 0-4 S is — 

 Activity at 27 _ 175 • 3 _ 

 Activity at 23 100 -5 * ' 



Hence activity for S at temperature 27 is — 



Theoretically (1) X (3) X activity at 23 for 0-4 S 

 = 2-5 X 1-74 X 100-5 = 437*2 c.mm. 

 Observed value = 436-0 ,, 



Example 3. — Temperature-variation from 21 to 29 . 

 Light changed from 0-4 S to S. 



Partial factor for temperature- variation at • 4 S is — 

 Activity at 29 236-5 



Activity at 21 88-5 



2*67 .. (4) 



