x Supplement to “ Nature,” June 9, 1923 

the mirror reflection of a right-handed screw is a left- 
handed screw, and the whole effect depends on a want 
of balance. In this case also there is a plane of 
cleavage, passing through the points where the 
molecules join each other end to end. 
Quartz is another example of a crystal possessing 
rotatory power, and like tartaric acid it contains a 
special element in its construction. The X-ray 
Fic. 16.—Spiral construction in quartz: large balls silicon, 
small balls oxygen. 
methods make this very clear, and give us also 
some indications as to the structural system. In 
the model shown in Fig. 16 the large balls represent the 
atoms of silicon and the smaller those of oxygen. The 
spiral character of the fundamental crystal is beauti- 
fully manifested in its outward form. The illustration 
(Fig. 17) shows the two possible forms of the crystal, 

Fic. 17.—Right- and left-handed quartz. 
right-handed and left ; a certain set of small faces gives 
to each crystal a spiral appearance. 
These various examples have been given as illustra- 
tions of the tasks which the new method of crystal 
analysis undertakes. They belong to a new field of 
research, akin to chemistry in that they seek to refer 
the properties of substances to the nature of the 
elements of construction. Chemistry has, however, 
concerned itself in the main with the relatively free 
molecules of liquids and gases: here we deal with 
the properties of the solid. Our concern is to explain 
the strength and elasticities of materials, their power 
of conducting electricity and heat, their electrical 


properties, optical properties: all these character- 
istics and many more, in terms of the structure 
as revealed by the X-ray analysis. Here are, we 
may say, the contributions of the method to pure 
science. 
It is natural to say something of the possible appli- 
cation to applied science. The properties of solid 
materials are of such fundamental interest to all arts 
and crafts that any new insight into their origin is 
necessarily important. But, at the same time, appli- 
cations of science to industry are always unexpected 
in nature and time. What we have now to do from 
the purely scientific side lies plain before us: how 
and when any result will have practical value cannot 
be foreseen. 
Much attention has been given to the immensely 
interesting problems of the crystallisation of iron and 
steel. Westgren in Sweden, Bain in America, and 
others, have done good work on the structure of the 
various forms of iron, a, 8, y, and 6. 
In Great Britain, the effect of the crystalline form — 
on the strength of a material has been examined by 
G. I. Taylor and Miss Elam in the case of the beautiful 
aluminium crystals of Prof. Carpenter. The crystals 
are very easy to deform because certain ,planes of 
easy slip traverse the whole crystal, and these planes 
are always the first to give way. The X-rays show 
the structure of the crystals and the position of the 
planes. When the large crystals are broken up into 
smaller, oriented in all ways, the material becomes - 
stronger because in whatever way a stress is brought — 
to bear some of the crystals are ready to bear it. 
Kaolinite, which can be examined, though in the” 
form of a very fine powder, shows clearly a crystalline 
structure: by the same methods it can be shown 
that the structure disappears when the temperature 
is raised to a certain point. These facts were, at 
- least in part, anticipated by the scientific branches of 
the pottery industry: but this method provides a 
useful confirmation, and further investigation promises — 
to be very interesting. Calcined at goo° C., a new 
crystalline structure appears: and when the tempera- 
ture has been sufficiently raised, the X-rays show that 
sillimannite has formed. 
Such examples are mere pointers in a-direction in 
which we may hope there will be a great movement 
in time to come. Our first aim is to develop the new 
methods as pure science. A broad, straight road 
opens out before us, and the going is good. As we 
travel along it we shall, doubtless, find many side — 
turnings leading to useful applications, but we must 
not expect them until we are right opposite to them. 
Our first and obvious duty is to travel down the 
high-road as far as it will take us. 
