526 
ON RECENT CHANGES IN 
Modern theoretical chemistry is conceded even by those who teach it to be 
in a condition far from satisfactory, but it is represented as having the recom¬ 
mendation that it approaches nearer than hitherto to the pure result of obser¬ 
vation, whilst certain practical advantages are believed to be brought in with it. 
The advocates of any new theory indeed ought to be able to show that 
benefit is to result from its adoption. If such is really the case here, no con¬ 
siderations of convenience alone ought to prevent the employment of that 
which is to do to science the very smallest service. As well might the astro¬ 
nomer reject the use of mathematics because it is a difficult study to those 
unlearned in such matters; or the physiologist reject the aid of chemistry 
because people generally know nothing of its principles. At the same time 
circumspection is necessary, lest, for the sake of mere ingenuity of conjec¬ 
ture, we be tempted to wander beyond legitimate bounds. 
In considering the views maintained by the majority of modern chemists, 
it ought to be some consolation to those of conservative tenets to reflect that 
the novelties in atomic weights, which have had so much to do in promoting 
the revolution, are in reality merely a readoption of nearly" the whole of 
those which were chosen and employed by Berzelius more than fifty years 
ago. 
The theoretical chemistry of to-day exhibits advantages and defects very 
similar to those attaching to the modern systems in natural history. Defini¬ 
tions are not in all cases intended to be absolute and liable to no exceptions, 
but can often be accepted only in a relative sense. Who, for instance, can in¬ 
dicate the boundary which separates the atomic and the so-called molecular 
mode of combination ? or can point out a group of compounds in which indi¬ 
vidual anomalies do not make their appearance? Nature, in fact, in my 
opinion, has always had the credit of working more by rule and with a 
greater degree of simplicity than we are justified in believing from what we 
see of her operations. 
The principal changes which have been made by modern chemists are in 
the atomic weights of a considerable number of the elements, and in the no¬ 
tation of formulae. Unfortunately, the nomenclature seems yet to be quite 
undecided. 
Before presenting the arguments which are employed in support of the exist¬ 
ing views with reference to the question of atomic weights, it will be necessary 
to examine the meaning attached by modern science to the word “ atom.” 
The possibility of the existence of such things as ultimate particles or physical 
atoms is for the metaphysician, rather than the student of natural philosophy, 
to decide. The existence of chemical atoms is at the present day regarded as a 
question not at all involved in that of the infinite divisibility of matter. 
Chemical atoms are defined as portions of matter incapable of further divi¬ 
sion by chemical agency, without inquiring what may be possible physically. 
If this be agreed upon, no hypothesis need be involved, atomic weights ac¬ 
cording to this definition being ascertained by appeal to experiment alone. 
If it is constantly found that a certain weight (or simple multiple of that 
weight) is concerned, in all the reactions into which we find a given element 
entering, the number expressing that proportion must be taken as represent¬ 
ing the quantity of matter in its chemical atom. Let us take the case of 
oxygen as an illustration : I shall first endeavour to give the chief chemical 
reasons which have influenced chemists in altering its atomic value from 
eight to sixteen, and then refer to the physical phenomena which lend sup¬ 
port to the idea. 
A very important question first presents itself—Is the oxygen of water divi¬ 
sible into two parts as the hydrogen is, or is it an indivisible quantity j in 
other words, is it composed of two atoms or one ? 
