Sept. 18, 1873] 
NATURE 
409 
ducts, every couple of materials is only exchanging half as fast 
as every couple of products. 
In fact you perceive that a determination of the proportion in 
which the substances are present in such a mixture will give us 
a measure of the relative velocities of those particular atomic 
motions ; and we may thus express our result :—The force of 
chemical combination is inversely proportional to the number of 
atomic interchanges, 
I cannot quit this part of our subject without alluding to the 
fact that some few chemists, of such eminence as to be entitled to 
the most. respectful attention, have of late years expressed an 
opinion that the idea of atoms is not necessary for the explana- 
tion of the changes in the chemical constitution of matter, and 
have sought as far as possible to exclude from their language any 
allusion to. atoms. 
Tt would be out of place on this occasion to enter into any 
discussion of the questions thus raised; but I think it right to 
point out :— 
I, That these objectors have not shown us any inconsistency 
in the atomic theory, nor in the conclusions to which it leads, 
Il. That neither these nor any other philosophers have been 
able to explain the facts of chemistry on the assumption that 
there are no atoms, but that matter is infinitely divisible. 
If. That when they interpret their analyses, these chemists 
allow themselves neither more nor less latitude than the atomic 
theory allows ; in fact, they are unconsciously guided by it. 
These facts need no comment from me, 
Our science grows by the acquisition of new facts which have 
an intelligible place among our ideas of the order of nature 3 but 
in proportion as more and more facts are arranged before us ia 
their natural order, in proportion as our view of the order of 
“nature becomes clearer and broader, we are able to observe and 
describe that order more fully and more -accurately—in fact, to 
improve our ideas of the order of nature. These more extensive 
and more accurate ideas suggest new observations, and lead to 
the discovery of truths which would have found no place in the 
narrower and less accurate system. Take away from Chemistry 
the ideas which connect and explain the multifarious facts ob- 
served, and it is no longer a science ; it is nothing more than a 
confused and useless heap of materials. 
_ The answer to our question respecting the meaning of the 
earnest work which is going on in our science must, I think, 
now be plain to you. Chemists are examining the combining 
properties of atoms, and getting clear ideas of the constitution 
of matter, 
Admitting, then, for the present, that such is the meaning of 
chem‘cal work, we have to consider the more important question 
of its use ; and I think you will agree with me that, in order to 
judge soundly whether and in what manner such a pursuit is 
useful, we have to consider its effect upon Man. What habits 
of mind does it engender? What powers does it develop ? 
Does it develop good and noble qualities and aspirations, and 
tend to make men more able and more anxious to do good to 
their fellow-men? Or is it a mere idle amusement, bearing no 
permanent fruits of improvement ? 
You will, I think, answer these questions yourselves if I can 
succeed in describing to you some of the chief qualities which 
experience has shown to be requisite for the successful pursuit of 
Chemistry, and which are necessarily cultivated by those who 
qualify themselves for such a career. 
One of the first requirements on the part of an investigator is 
accuracy in observing the phenomena with which he deals. He 
must not only see the precise particulars of a process as they 
present themselves to his observation ; he must also observe the 
order in which these particular appearances present themselves 
under the conditions of each experiment. No less essential is 
accuracy of memory. An experimental inquirer must remember 
accurately a number of facts ; and he needs to remember their 
mutual relations, so that one of them when present to his mind 
may recall those others which ought to be considered with it. In 
fact, he cultivates the habit of remembering facts mainly by their 
place in nature. Accuracy in manual operations is required in 
all experimental inquiries ; and many of them afford scope for 
very considerable skill and dexterity. 
These elementary qualities are well aknown to be requisite for 
success in experimental science, and to. be developed by careful 
practice of its methods ; but some higher qualities are quite as 
necessary as these in ail but the most rudimentary manipulations, 
and are,developed in a remarkable degree by the higher work of 
science, i : “ 
Thus it is of importance to notice that a singularly good 
training in the accurate use of words is afforded by experimental 
chemistry. 
whether he be a first-year’s student who wants to find the con- 
stituents of a common salt, or whether he be the most skilled and 
experienced of chemists, seeks beforehand to get such information 
from the records of previous observations as may be most useful 
for his purpose. 
medium of words ; and any failure on his part to understand the 
precise meaning of the words conveying the information requisite 
for his guidance is liable to lead him astray. Those elementary 
exercises in analytical chemistry, in which brief directions to the 
students alternate with their experiments and their reports of 
experiments made and conclusions drawn, afford a singularly 
effective training in the habit of attending accurately to the 
Everyone who is about to enter on an inquiry, 
This information he obtains through the 
meaning of words used by others, and of selecting words capable 
of conveying without ambiguity the precise meaning intended. 
Any inaccuracy in the student’s apprehension of the directions 
given, or in the selection of words to describe his observations 
and conclusions, is at once detected when the result to which 
he ought to have arrived is known beforehand to the teacher. 
Accuracy of reasoning is no less effectively promoted by the 
work of experimental chemistry. It is no small facility to us 
that the meaning of the words which we use to denote proper- 
ties of matter and operations can be learnt by actual observation. 
Moreover each proposition comprised in chemical reasonings 
conveys some distinct statement susceptible of verification by 
similar means ; and the validity of each conclusion can be tested, 
not only by examining whether or not it follows of necessity from 
true premisses, but also by subjecting it to the independent test 
of special experiment. . 
Chemists have frequent occasion to employ arguments which 
indicate a probability of some truth ; and the anticipations based 
upon them serve as guides to experimental inquiry by selecting 
crucial tests. But they distinguish most carefully such hypotheses 
from demonstrated facts. 
Thus a pale green solution, stated to contain a pure metallic 
salt, is found to possess some properties which belong to salts of 
Tron. Nothing else possesses these properties except salts of 
Nickel ; and they manifest a slight difference from Iron salts in 
one of the properties observed. 
The analyst could not see any appearance of that peculiarity 
which distinguishes Nickel salts; so he concludes that he has 
probably got iron in his solution, but almost certainly either Iron 
or Nickel. THe then makes an experiment which will, he knows, 
give an entirely different result with Iron salts and Nickel salts ; 
and he gets very distinctly the result which indicates Iron, 
Having found in the green liquid properties which the presence 
of Iron could alone impart, he considers it highly probable that 
Tron is present. But he does not stop there ; for, although the 
facts before him seem to admit. of no other interpretation, he 
knows that, from insufficient knowledge or attention, mistakes 
are sometimes made in very simple matters. The analyst there. 
fore tries as many other experiments as are known to distinguish 
Iron salts from all others ; and if any one of these leads distinctly 
toa result at variance with his provisional conclusion, he goes 
over the whole inquiry again, in order to find where his mistake 
was. Such inquiries are practised largely by students of che- 
mistry, in order to fix in their minds, by frequent use, a knowledge 
of the fundamental properties of the common elements, in order 
to learn by practice the art of making experiments, and, above 
all, in order to acquire the habit of judging accurately of evidence 
in natural phenomena, Such a student is often surprised at 
being told that it is not enough for him to conduct his experi- 
ments to such a point that every conclusion except one is con- 
trary to the evidence before him—that he must then try every 
confirmatory test which he can of the substance believed to le 
present, and ascertain that the sample in his hands agrees, as fur 
as he can see, in all properties of the known substance of which 
he believes it to be a specimen. 
Those who tread the path of original inquiry, and add to 
human knowledge by their experiments, are bound to practise 
this habit with the most scrupulous fidelity and care, or may 
and graye will be the mistakes they will make. 
Thus a chemist thinks it probable tha> he might prepare some 
well-known organic body of the aromatic family by a new process, 
He sets to work and obtains a substance agreeing in appearance, 
in empirical composition, in molecular weight, and in mary 
other properties with the compound which he has in view. [I> 
is, however, not satisfied that his product is a sample of that 
