70 MACHINERY FOR MAKING THIN SECTIONS OF MINERALS. 
of rock material, of large size, as well as in small frag- 
ments, with precision, economy of material, and rapidity, 
the lecturer exhibited and described a machine, devised 
in large manner by himself, which is adapted to accom- 
plish these objects. 
Several years ago, a slicing machine was devised by 
Professor James Hall, the eminent State Geologist, with 
the assistance of his son. This was a long distance 
ahead of the ineffective and crude ‘‘lapidary’s lathe ”’ 
used by most scientists who make rock sections. 
This machine has been used in the State Geological 
Survey, and very large and fine sections of fossils have 
been made by it with considerable facility. It was not, 
however, adjustable, so as to cut desired planes with suf- 
ficient precision and delicacy, and the adjustments of 
which it was capable consumed much more time and 
work than was either necessary or desirable. There was 
too much waste of both time and of valuable material in 
its use. Nevertheless, it was a great step in advance ; 
the main principle of its construction is very probably 
the very best that can be devised; only its capabilities 
were not worked up sufficiently into the details of exact 
work. 
The lecturer, finding some machine of this kind abso- 
lutely necessary for his own paleontological work, but 
finding also that the Hall machine would not accomplish 
what was desired with sufficient exactness, undertook, 
as a matter of necessity rather than of choice, to 
start with this good basis of a practical machine already 
devised and working it up in detail, to produce some- 
thing which might more or less deserve the name of an 
instrument of precision. He, however, acknowledged, 
most heartily and gratefuily, his indebtedness to Profes- 
sor James Hall and his son for the fundamental ideas and 
movements which have made it possible to elaborate an 
instrument which can do precise and economical work. 
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