140 THE ROYAL SOCIETY OF CANADA 
at the fifth stage of the tests, when C alone was mixed with D alone, that 
the above exceedingly probable conclusion was shown to be an error. 
This case illustrates too the converse fact that it is necessary in 
science to investigate improbable conclusions with the same thorough- 
ness as those that are probable. It seemed very improbable that a 
combination of colorless liquids could produce color, and yet by ex- 
haustive examination this improbable conclusion was shown to be, in 
point of fact, correct. 
ii. A NECESSARY CONCLUSION IS A CONCLUSION WHICH ONE IS 
REQUIRED, AS A REASONABLE MAN, TO ACCEPT. 
Illustration: —A student is given two liquids, B and C, having each 
the colorless appearance of water, and he is asked whether a combina- 
tion of them will produce a mixture with color. (1) Into a quantity 
of B he pours suddenly a quantity of C, and the result is a colorless 
liquid. He now, however, (2) takes a fresh quantity of B and adds to 
it gradually a quantity of C. As he pours slowly from C into B the 
mixture presently becomes colored, but as he continues the addition of 
C this color again disappears, and the mixture is restored to a colorless 
liquid. B and C are potassium iodide and mercury chloride, KI and 
HgCl,, which give a scarlet precipitate soluble in excess of either. 
In this case the student, having made the first and rougher test of 
mixing B and C suddenly in indeterminate quantities, was not required 
as a reasonable man to accept the result as decisive. The test proved 
indeed that a mixture of the two liquids in the proportions actually 
used remained colorless. It was, however, not unreasonable to suppose 
that a mixture in other proportions might nevertheless produce color. 
Therefore the result of the first test, though it afforded ground for a 
very probable conclusion that a mixture of the liquids would not 
produce color, did not establish for the student a necessary conclusion, 
i.e., one which he was required as a reasonable man to accept. On the 
contrary he was required as a reasonable man to proceed to the second, 
more accurate test; and the result illustrates afresh how essential it is 
in science that nothing short of necessary conclusions be accepted. 
lil. A CORRECT PROCESS IS ONE THAT RIGHTLY FOLLOWED LEADS 
NECESSARILY TO A CORRECT RESULT. 
Illustrations: —In the cases of the two students with the three 
and two liquids respectively the process of examination adopted, of 
actually mixing the liquids, was correct. Had they confined themselves 
to mere theorizing as to whether colorless liquids could produce color, 
they could never have reached a conclusion that would necessarily be 
