THE ADDRESS OF THE PRESIDENT. 
GEO. W. STEWART. 
As President of the Academy I now haye the honor to present 
an address, thus reestablishing a former custom, but with ap- 
propriate regard for the necessity of brevity. Within the time 
of twelve minutes I propose to glance at recent progress in 
physics and also to discuss the function and responsibility of this 
Academy, The notable achievements in that science within the 
past few years cannot all receive mention hence it is essential 
that there be pointed out but a few typical cases of progress. 
One of the most interesting advances has been an extension 
of our. knowledge of crystal structure, this being made possible 
by X-ray analysis. Not only can the distance between planes 
be measured but, in the case of compounds like sodium chloride, 
the distribution of the constituent atoms can be ascertained. 
The significant result is that, in almost all crystals investigated, 
there is at each lattice point not a molecule but an atom. Thus 
in the crystal of sodium chloride, the sodium and chlorine atoms 
are each arranged according to a simple cubic lattice, but the 
two lattices are arranged so that each atom is surrounded by 
six equidistant atoms of the other kind. Thus at no point in 
the crystal of sodium chloride do we find what we have for- 
merly conceived to be a molecule of that substance. Similar re- 
sults are found with crystals of other compounds. It is yet too 
early to appreciate the full significance of these discoveries with 
crystals, but we can now at least opine that our conception of 
the molecule must meet with a very definite revision. 
The study of X-ray radiation has served another and perhaps 
more important function, for it has led us to see that the funda- 
mental characteristic of an element is not its atomic “'weight” 
but rather its atomic number which is approximately one-half 
of its atomic weight. This is very clearly proved by the re- 
lationships between the X-ray radiations which are characteristic 
of the various elements and constitutes one of the most important 
recent advances made in our knowledge of atomic structure. 
But what is the present conception of the physicist concern- 
ing the constitution of the atom? For many years the spectra 
