50 SECTIONAL ADDRESSES 
equally natural that such attempts should be made quite independently 
by a number of workers. 
With renewed interest in the subject, advances in the technique of 
microscopic examination were rapid. The first development was E. C. 
Jeffrey’s combination of maceration with section-cutting. He treated 
very small blocks of coal for long periods with hydrofluoric acid, thereby 
removing the mineral matter and so far softening the substance that it 
could be sectioned on the microtome like a modern plant. By this method 
sections may be prepared which show much detail with surprising clear- 
ness. _ Its limitations are the small size of the blocks which can be success- 
fully treated, the liability to tearing of the more delicate portions of the 
coal by even the smoothest razor, and a doubt whether the finer structures 
are not in some degree obliterated by the maceration. While its results 
were a very great advance on the earlier efforts at direct section-making 
by grinding, they are not equal to some of the more recent products of 
the latter method. 
Direct cutting was developed to a high degree of efficiency by Reinhardt 
Thiessen in America and by the late Mr. James Lomax in this country. 
The former aimed, in the first instance, at getting sections of moderate 
size, but of such extreme thinness that the finest details could be studied 
with the highest magnifications. ‘The latter was the pioneer in the 
preparation of large sections, which made possible the examination of an 
entire coal-seam in a moderate number of slices. In the early stages 
these large sections were naturally made with some sacrifice of thinness 
and uniformity, but increasing experience has made possible the attain- 
ment of these features in even the largest sections. 
Simultaneously with the foregoing developments an entirely new 
method of examination was introduced in Germany by H. Winter—namely, 
the examination by reflected light of polished and etched surfaces of coal. 
This method has been developed with conspicuous success in this country 
by Mr. C. A. Seyler, and is extensively used by many workers on the 
Continent. The vividness with which many fine details of plant structure 
in the coal are revealed by this method can only be described as startling ; 
and one of its advantages is that, by variation of the methods of polishing 
or etching, different features can to some extent be revealed at will. The 
size of surface which can be examined is, of course, almost unlimited, 
and a few minutes is sufficient for its preparation. For the examination 
of the complete section of a seam it has obviously great advantages. At 
the same time it must be observed that the character of a good deal of the 
coal substance remains obscure, and the interpretation of the structures 
actually seen can be securely attempted only by close comparison of the 
etched picture with actual thin sections. Used in conjunction, the two 
methods of examination afford a means by which the whole story of a coal 
seam may be deciphered with accuracy and comparative rapidity. 
What have been the results of all the attempts to study the microscopic 
structure of coal ? 
The * Uniform Brown Substance.’—Before the time of Witham and 
Hutton coal was often regarded as a deposit from ‘ solution’ in water— 
as a kind of vegetable ‘ extract,’ which might consequently be expected to 
