PRESIDENTIAL ADDRESS. 493 
somewhat modified, though not essentially, by the attachment of the others; 
and that the space formule of chemistry have more than analogical 
significance.’ And again in the following passage, in which a far-reaching 
confession is made: ‘The aim of structural chemistry must go much 
deeper (than dynamical methods of treatment); and we have found it 
difficult, on the physical evidence, to gainsay the conclusion that the 
molecular architecture represented by stereo-chemical formule has a 
significance which passes beyond merely analogical representation and 
that our dynamical views must so far as possible be adapted to it.’ The 
remark made by Helmholtz in one of his letters, ‘that organic chemistry 
progresses steadily but in a manner which, from the physical standpoint, 
appears not to be quite rational,’ must be regarded as little more than a 
confession that he was out of his depth. When properly understood, 
nothing could be more rational and logical than the way in which our 
theory of structure has been gradually built up on an impregnable basis 
of fact, with the aid of the very simple conceptions of valency postulated 
by Frankland and Kekulé. Our security lies in the fact that the postulates 
of our theory have been tested in an almost infinite variety of cases and 
never found wanting; this is not to say they are applicable in all cases, 
but merely that whenever we are in a position to apply them we can do so 
without hesitation. Larmor refers to the habit of physicists of taking 
comfort in Helmholtz’s remark ; it will be well if instead they make them- 
selves acquainted with our methods and with the results we have won, with 
a minimum of speculative effort, by the cultivation of an instinct or sense 
of feeling which experience shows to be an effective guide to action. Now 
that physical inquiry is largely chemical, now that physicists are regular 
excursionists into our territory, it is essential that our methods and our 
eriteria should be understood by them. I make this remark advisedly, as it 
appears to me that, of late years, while affecting almost to dictate a policy to 
us, physicists have taken less and less pains to make themselves acquainted 
with the subject-matter of chemistry, especially with our methods of arriving 
at the root-conceptions of structure and of properties as conditioned by 
structure. It is a serious matter that chemistry should be so neglected by 
physicists and that the votaries of the two sciences should be brought so little 
into communion. 
The central luminary of our system, let me insist, is the element carbon. 
The constancy of this element—the firmness of its affections and affinities— 
distinguishes it from all others. It is only when its attributes are under- 
stood that it is possible to frame any proper picture of the possibilities which 
lie before us, of the place of our science in the Cosmos. As Longfellow 
sings of the sea in his poem ‘ The Secret of the Sea,’ ‘ Only those who brave 
its dangers comprehend its mystery ’—only those who are truly conversant 
with the root conceptions of organic chemistry are in a position to attempt 
the interpretation of the problems of our science as a whole or even to 
understand the framework upon which it is built up. And yet we continue 
to withhold the knowledge of the properties of carbon from students until 
a late period of their development ; indeed, when I insisted recently that - 
organic and inorganic chemistry should be taught as one subject to medical 
students,’ I was told that it could not be; that the attempt had been made 
with disastrous consequences. I trust that ere long the futility of such an 
attitude will be generally realised. 
It is remarkable how much our conceptions are now guided by geo- 
metrical considerations. The development by van’t Hoff of the Pasteur 
hypothesis of geometrical asymmetry has been attended with far-reaching 
**The Reform of the Medical Curriculum,’—Science Progress, January and 
April 1907, 
