i879-} 
British Association. 
639 
is because there exists a practical distinction separating the 
investigation of exaCt science into two well-marked classes when 
they are viewed, not as they are in themselves, but in their rela- 
tion to the powers of us human beings. All valid investigations 
in exadt science appeal to what can be direcftly perceived, and 
all lead to a conclusion which can be reasoned out from it ; but 
there are some of these investigations in which the main 
difficulty consists in making the appeal to the senses, and there 
are others in which the main difficulty lies in the process of 
reasoning. 
To contend with these difficulties successfully requires very 
different qualities of mind and body. In experimental science 
the powers principally called into requisition are readiness and 
closeness of observation, dexterity in manipulation, skill in 
devising expedients, accuracy in making adjustments, and great 
patience. It also requires that the investigator should have an 
accurate memory of what else he has witnessed resembling the 
phenomenon under observation, that he should be quick to 
detecft every point of agreement and difference that can be 
perceived, and be skilful to seledt those which are significant, 
and to employ them as materials for provision to guide his 
further proceedings. But the strain on the reasoning powers is 
generally less, often of trifling amount. The question is put to 
Nature, and it is Nature usually that gives the bulk of the 
answer. The most striking monument of splendid achieve- 
ments by the experimental method of investigation unaided 
by the dedudtive method is to be found in the science of 
chemistry. 
An equally typical instance of the power of the dedutftive 
method is the science of mechanics. This science, which has 
sunk deeper into the secrets of Nature than any other science, 
and which is the science towards whom all other physical 
sciences are at present more or less gravitating, is essentially 
dedudtive. There is little or no difficulty about its fundamental 
data. They are facfts of Nature so patent to all men, and so 
indelibly implanted in human conception, that some persons 
have supposed that we have an intuitive perception of them. 
But, while the materials from which the mind is to work are 
thus easily obtained, it has taxed to the utmost the reasoning 
powers of understandings like Newton’s to evolve the few con- 
sequences of them which are already known, and the investigator 
has to call to his assistance every aid to prolonged consecutive 
thought which mathematicians can devise. 
No reach of intellect applied to the materials in existence 
i before i860 could have elicited the facft that iron exists upon the 
I sun. This great discovery was made by Professor Kirchhoff, 
a scientific man who was equally versed in both methods of 
| investigation. It was the experimental method he employed. 
Kirchhoff’s great merit and the real difficulty of his work lay in 
VOL. IX. (N.S.) S 2 
