se 
Sept. 18, 187 3] 
Nobly would Joule have discharged the duties of President 
had his bodily health been equal to the task; but it became 
apparent after a while that he could not rely upon sufficient 
strength to justify him in performing the duties of the Chair, 
and, in obedience to the orders of his physician, he placed his 
resignation in the hands of the Council about two months ago. 
When, under these circumstances, the Council did me the great 
honour of asking me to accept their nomination to the President- 
ship, T felt that their request ought to have with me the weight 
of a command, i 
For a good many years past Chemistry has been growing ata 
more and more rapid rate, growing in the number and variety 
of facts which are added to its domain, and not Jess remarkably 
in the clearness and consistency of the ideas by which these facts 
are explained and systematised. The current literature of che- 
mical research extends each year to the dimensions of a small 
library ; and mere brief extracts of the original papers published 
annually by the Chemical Society, partly aided by a grant from 
this Association, take up the chief part of a very stout volume. 
I could not, if I would, give you to-night even an outline of the 
chief newly discovered compounds and of the various changes 
which they undergo, describing each of them by its own name 
(often a very long one) and recording the specific properties 
which give to each substance its highest scientific interest. But 
_ Tam sure that you would not wish me to do so if I could ; for 
we do not meet here to study chemistry; I conceive that we 
meet here for the purpose of considering what this wondrous ac- 
tivity in our science means, what is the use of it, and, true to 
our object as embodied in the name of this Association, to con- 
sider what we can do to promote the Advancement of Science. 
I propose to lay before you some facts bearing on each of these 
questions, and to submit to you some considerations respecting 
them. 
In order to ascertain the meaning of the work which has been 
going on in chemistry, it will, I think, be desirable for us to 
consider the leading ideas which have been in the minds of 
chemists, and which guide their operations. 
Now, since the father of modern chemistry, the great Dalton, 
gave to chemists a firm hold of the idea of Atoms, their labours 
have been continually guided by that fundamental idea, and have 
confirmed it by a knowledge of more and more facts, while at 
the same time steadily adding to our knowledge of the properties 
of atoms. Every chemist who is investigating a new compound 
takes for granted that it must consist of a great number of atom- | 
NATURE 
clusters (called by him molecules), all of them alike, and each | 
molecule consisting of a certain number of atoms of at least two 
kinds. One of his first endeavours is to ascertain how many 
atoms of each kind there are in each molecule of the compound. 
I must not attempt to descrive to you the various kinds of expe- 
riment which he performs for the purpose of getting this informa- 
tion, how each experiment is carried out with the aid of delicate 
instruments and ingenious contrivances found by long experience 
to enable him to obtain the most trustworthy and accurate re- 
sults ; but I want to draw your attention to the reasoning by 
which he judges of the value of such experiments when they 
agree among themselves, and to the meaning which he attaches 
to their result. 
If the result of his experiments does not nearly agree with any 
atomic formula (that is, if no conceivable cluster of atoms of the 
kinds known to be in the compound would on analysis give such 
results as those obtained), the chemist feels sure that his experi- 
ments must have been faulty: either the sample of substance 
which he worked upon contained foreign matter, or his analyses 
were not made with due care. He sets to work again, and goes 
on till he arrives at a result which is consistent with his know- 
ledge of the combining-properties of atoms. It is hardly neces- 
sary to say that even the best experiment is liable to error, and 
that even a result obtained with the utmost care cannot be ex- 
pected to afford more than an approximation to the truth. 
Every good analysis of a pure compound leads to results which 
approximate to those required by the Atomic Theory ; and che- 
mists trust so thoroughly to the truth of that guide, that they 
correct the results of such analysis by the aid of it. 
The chemical idea of atoms serves for two purposes :— 
1, It gives a clear and consistent explanation of an immense 
number of facts discovered by experiment, and enables us to 
compare them with one another and to classify them. 
2, It leads to the anticipation of new facts, by. suggesting new 
compounds which may be made ; at the same time it teaches us 
that no compounds can exist with their constituents in any other 
; 407 
than atomic proportions, and that experiments which may imply 
the existence of any such compound are faulty. 
We have the testimony of the great Berzelius to the flood of 
light which the idea of atoms at once threw on the facts respect: 
ing combining proportions which had been accumulated before 
it was made known ; and from that time forward its value has 
rapidly increased as each succeeding year augmented the num- 
ber of facts which it explained. 
Allow me at this point of my narrative to pause for a moment 
in order to pay a tribute of respect and gratitude to the memory 
of one who has recently passed from among us, and who in the 
time of his full activity was a leader of the discoveries of new 
facts in the most difficult part of our science. Liebig has been 
generally known in this conntry through his writings on agricul- 
tural chemistry, through his justly popular letters on chemistry, 
and other writings, by means of which his brilliant intellect and 
ardent imagination stimulated men to think and to work. Among 
chemists he was famed for his numerous discoveries of new or- 
ganic compounds, and their investigation by the aid of improved 
-methods ; but I believe that the greatest service which his genius 
rendered to science was the establishment of the chemical school 
of Giessen, the prototype of the numerous chemical schools for 
which Germany is now so justly celebrated. I think it is not 
too much to say that the Giessen laboratory, as it existed some 
thirty years ago, was the most efficient organisation for the pro- 
motion of chemistry which had ever existed. 
Picture to yourselves a little community of which each member 
was fired with enthusiasm for learning by the genius of the great 
master, and of which the best energies were concentrated on the 
one object of experimental investigation. 
The students were for the most part men who had gone through 
a full curriculum of ordinary studies at some other University, 
and who were attracted from various parts of the world by the 
fame of this school of research. 
Most of the leading workers of the next generation were pupils 
of Liebig ; and many of them have established similar schools of 
research. 
We must not, however, overlook the fact that Liebig’s genius 
and enthusiasm would have been powerless in doing this admir- 
able work, had not the rulers of his Grand-Duchy been enligh- 
tened enough to know that it was their duty to supply him with 
the material aids requisite for its successful accomplishment. 
Numberless new compounds have been discovered under 
the guidance of the idea of atoms; and in proportion as our 
knowledge of substances and of their properties became more 
extensive, and our view of their characteristics more accurate and 
general, were we able to perceive the outlines of their natural 
arrangement, and to recognise the distinctive characteristics of 
various classes of substances. I wish I could have the pleasure 
of describing to you the origin and nature of some of these ad- 
mirabie discoveries, such as homologous series, types, radicals, 
&c. ; but it is more to our purpose to consider the effect which 
they had upon the idea of atoms, an idea which, still in its in- 
lancy, was plunged into the intellectual turmoil arising from a 
variely of novel and original theories suggested respectively by 
independent workers as best suited for the explenation of the 
particu'ar phenomena to which their attention was mainly 
directed. 
Each of these workers was inclined to attach quite sufficient 
importance to his own new idea, and to sacrifice for its sake any 
other one capable of interfering with its due development. 
The father of the atomic theory was no more ; and the little 
infant had no chance of life, unless from its own sterling merits 
it were found useful in the work still going on. 
What then was the result? Did it perish like an ephemeral 
creation of human fancy ? or did it survive and gain strength by 
the inquiries of those who questioned Nature and knew how to 
read her answers? 
Although snticipating my answer to these questions, you will 
probably be surprised to hear the actual result which I have to 
record, a result so wonderful that the more I think of it the more 
I marvel at it. Not only did these various theories contain 
nothing at variance with the atomic theory ; they were found to 
be natural and necessary developments of it, and to serve for 
its application to a variety of phenomena which were unknown 
to its founder. 
Among the improvements of our knowledge of atoms which 
have taken place, I ought to mention the better evaluations ot 
the relative weight of atoms of different kinds, which have been 
made since Dalton’s time. More accurate experiments than 
