186 W. M. HAMLET. 
matter is heterogeneous and discontinuous. In the case of 
the metals used in building construction, the apparent 
arrangement of the particles is either crystalline, fibrous, 
porous or granular as the case may be, and was usually 
obtained by the fracture, bending or torsion of the specimen. 
Although it was well known that toughness, hardness, 
brittleness, strength and elasticity were correlated to the 
visible grain or appearance of the fractured surfaces of the 
metal, yet the new method confirmed this and showed that 
strength and elasticity might be deduced from the minute 
microscopic structure of the sample to be tested, from 
which follows the discrimination between good and bad 
materials. So rapid has been the success of the examin- 
ation that a journal has come into existence dealing with 
this branch of metal testing called the ‘ Metallographist.’ 
It is found in practice the best, i.e., the most durable 
materials are those of even texture that is to say those of 
the most homogeneous structure. Strictly speaking even 
these are heterogeneous, but provided the structure be 
small, dense, and of uniform texture to the eye, or to an 
eye assisted by a magnifying power of seventy or eighty 
diameters, it may be provisionally or for all practical pur- 
poses be termed homogeneous. In many materials the 
process of what is known as annealing is nothing more than 
the application of heat with a view of breaking up what 
was once a coarse-grained crystalline structure and by slow 
cooling allow the molecule to set in uniform evenly placed 
positions. 
Where different metals are present together, as in the 
case of an alloy, if the structure be irregular, coarse, and 
highly granular, then the metals having differing electric 
potentials under the action of an exciting liquid will set up 
short voltaic circuits and show corrosion: that is to say an 
electro-positive and an electro-negative metal in juxta- 
