646 
lay before you a sketch of the present position of 
certain branches of chemical knowledge and to discuss 
the directions in which progress is to be sought; 
none of us dare cherish the conviction that his views 
on such matters are correct, but everyone desirous of 
contributing towards the development of his science 
must attempt an appreciation of this kind. The im- 
portance to the worker and to the subject of free 
ventilation and discussion of the point of view taken 
by the individual can scarcely be over-estimated. 
The two sciences of chemistry and physics were at 
one time included as parts of the larger subject en- 
titled natural philosophy, but in the early part of the 
nineteenth century they drew apart. Under the 
stimulus of Dalton’s atomic theory, chemistry de- 
veloped into a study of the interior of the molecule, 
and, as a result of the complication of the observed 
phenomena, progressed from stage to stage as a 
closely reasoned mass of observed facts and logical 
conclusions. Physics, less entangled in its infancy 
with numbers of experimental data which apparently 
did not admit of quantitative correlation, was de- 
veloped largely as a branch of applied mathematics, 
such achievements of the formal physics of the last 
century as the mathematical theory of light and the 
kinetic theory of gases are monuments to the powers 
of the human intellect. 
The path of chemistry, as an application of pure 
logical argument to the interpretation of complex 
masses of observations, thus gradually diverged from 
that taken by physics as the mathematical treatment 
of less involved experimental! data, although both 
subjects derived their impetus to development from the 
speculations of genius. 
It is interesting to note, however, that during recent 
years the two sciences, which were so sharply dis- 
tinguished twenty years ago as to lead to mutual 
misunderstandings, are now converging. Many 
purely chemical questions have received such full 
quantitative study that the results are susceptibie to 
attack by the methods of the mathematical physicist ; 
on the other hand, the intense complication perceived 
during the fuller examination of many physical pro- 
lems, has led to their interpretation by the logical 
argument of the chemist because the traditional mathe- 
matical mode of attack of the phycisist has proved 
powerless to deal with the intricacies exhibited by 
the observed facts. 
The progress of chemistry during the last century 
has been mainly the result of the coordination of 
observed facts in accordance with a series of hypo- 
theses each closely related in point of time to the one 
preceding it. The atomic theory, as it was enunciated 
by Dalton in 1803, was a great impetus to chemical 
investigation, but proved insufficient to embrace all 
the known facts; it was supplemented in 1813 by 
Avogadro’s theorem—that equal volumes of gases 
contain the same number of molecules at the same 
temperature and pressure. These two _ important 
theoretical developments led to the association of a 
definite physical meaning with the idea of molecular 
composition, but ultimately proved insufficient for the 
interpretation of the ever-increasing mass of chemical 
knowledge collected under their stimulus. A further 
great impetus followed the introduction by Frank- 
land and Kekulé, in 1852 onwards, of the idea of 
valency and the mode of building up constitutional 
formule; the conception of molecular constitution 
thus arose as a refinement on the Daltonian notion of 
molecular composition. In course of time the theor- 
etical scheme once more proved insufficient to accom- 
modate the accumulated facts, until, in 1874, van ’t 
Hoff and Le Bel demonstrated the all-important part 
which molecular configuration plays in the interpreta- 
NO., 2338) VOrsost 
NATURE 
[AuGUST 20, 1914 
| means of which 
tion of certain classes 
organic chemist. 
During the early days of chemical science—those 
of Dalton’s time and perhaps also those of Frankland 
and Kekulé—we can believe that chemical theory may 
have lacked the physical reality which it now seems 
to us to present; the attitude of our predecessors to- 
wards the theoretical interpretation of their observa- 
tions was rather that described by Plato: ‘‘as when 
men in a dark cavern judge of external objects by 
the shadows which they cast into the cavern.’ In 
the writings of the most clear-sighted of our fore- 
runners we can detect an underlying suspicion of a 
possibility that, at some time or other, the theory by 
chemical observations are held to- 
gether may undergo an entire reconstruction; a very 
few years ago Ostwald made a determined attempt 
to treat our science without the aid of the molecular 
hypothesis, and indeed suggested the desirability of 
giving the Daltonian atomic theory decent burial. 
The last ten years or so has seen a change in this 
attitude. The development of organic chemistry has 
revealed so complete a correspondence between the 
indications of the conception of molecular constitution 
and configuration and the observed facts, and recent 
work on the existence of the molecule, largely in 
connection with colloids, with radioactivity, and with 
crystal structure, is so free from ambiguity, that per- 
sistence of doubt seems unreasonable. Probably 
most chemists are prepared to regard the present 
doctrine of chemical constitution and configuration 
as proven; although they may turn a dim vision 
towards the next great development, they have few 
misgivings as to the stability of the position which 
has already been attained. 
Let us consider how far the study of organic chem- 
istry has hitherto led us; we may pass over the 
gigantic achievements of those who in past genera- 
tions determined constitution and performed syntheses, 
thus making the subject one of the most perfect 
examples of scientific classification which exist, and 
turn to the question of molecular configuration. In 
1815 Biot observed that certain liquid organic sub- 
stances deflect the plane of polarisation of a trans- 
mitted ray of light either to the right or to the left; 
half a century later Pasteur and Paterno pointed the 
obvious conclusion, namely, that the right- or left- 
handed deviation thus exerted must be due to a 
corresponding right- or left-handedness in the con- 
figuration of the chemical molecule. A scheme repre- 
senting such right- or left-handedness, or enantio- 
morphism, was first enunciated by van ’t Hoff and 
Le Bel upon the basis of the previously established 
doctrine of chemical constitution; briefly stated, the 
idea suggesed was that the methane molecule, CH,, 
was not to be regarded as extended in a plane in the 
manner represented by the Frankland-Kekulé con- 
stitutional formula, but as built up symmetrically in 
three-dimensional space. The carbon atom of the 
methane molecule thus occupies the centre of a 
regular tetrahedron, of which the apices are replaced 
by the four hydrogen atoms. A methane derivative, 
in which one carbon is separately attached to four 
different univalent atoms or radicles of the type 
CXYZW, should thus exist in two enantiomorphous 
configurations, one exhibiting right- and the other 
left-handedness. The inventors of this daringly 
mechanistic interpretation of the far less concrete 
constitutional formulz were able to interpret im- 
mediately a large number of known facts, previously 
incomprehensible, by means of their extension of the 
Frankland-Kekulé view of constitution. They showed 
that every substance then known, which in the liquid 
state exhibited so-called optical activity, could be 
of phenomena known to the 
