certainly metallic, and very heavy He united the idea of 
weight with that of metal, and the evidence of his senses having 
been insufficient to dissever ideas so inseparably associated in 
his mind, he mistook his judgment of the ponderosity of the 
substance for his sensation of it.* Of course, therefore, in the 
same degree as we mingle observation and inference in the record 
ot what professes to be observation only, the evidence afforded 
is in the same degree invalidated. The first step then is to 
sever the one from the other, and see that our facts be true. 
1 do not mean, in what I have said, to imply that in the 
accumulation of evidence we ought, if possible, to keep our 
mental action wholly in abeyance, and observe indiscriminately 
all tacts that come before us. It is most useful to have some 
suggestive hypothesis to guide our observations, in order that 
leie may be method in our investigations, and to enable us to 
select for more careful scrutiny the more important circum- 
stances. A certain amount of deductive reasoning must accom- 
pany the student from the first, if he would not accumulate his 
facts blindfold. I quite agree with what Hooke says in his 
work on Philosophical Method, that « the natural philosopher 
ought to be very well skilled in those several kinds of pliilo- 
sophy already known, to understand their several hypotheses, 
suppositions, observations, &c., their various ways of ratiocina- 
tions and proceedings, the several failings and defects, both in 
their way of raising, and in their way of managing their several 
theories, for by this means the mind will be somewhat more 
leady at guessing at the solution of many phenomena almost at 
first . sight, and thereby be much more prompt at makin°- 
queries, and at tracing the subtlety of nature, aud in discovering 
and reaching into the true reason of things.” What I may call 
the suggestively deductive method, accompanied by continuous 
observation— has accumulated more valuable and systematic 
evidence than any other, and has yielded most important 
results. The investigator in such a case uses “ such facts as 
are in the first place known to him, in suggesting probable 
hypotheses; deducing other facts, which would happen if a 
particular hypothesis be true, he proceeds to test the truth of 
his notion by fresh observations or experiments. If any result 
prove different from what he expects, it leads him either to 
abandon or to modify his hypothesis; but every new fact may 
give some new suggestion as to the laws in action. Even if the 
* This paper having been written away from books, I have not been able 
lS4Slt» am<IUOtmg ’ n0raIWay8 t0 rcfa known quotations to 
