RECENT PROGRESS IN PHYSICAL SCIENCE. 
INSTRUMENTS. 
BY 
C. F. Marvin. 
Recent progress in instrumental physics can hardly be 
fairly presented in so brief a communication as this must 
necessarily be, and we can attempt, therefore, to mention 
only a few steps of progress to which perhaps some special 
interest attaches. 
Progress, regarded from a comprehensive point of view, 
is generally a natural growth extending over considerable 
periods of time, and in a study of the present state of any 
branch of knowledge we must deal with the ultimate result 
of all past effort expended in any given direction. We will 
have before us in each instance the product of an evolution, 
and very often the exact contribution of a given year cannot 
be fully differentiated or recorded. On the other hand, 
progress is sometimes strikingly spasmodic. Development 
in a given direction seems almost to be arrested for a time, 
only to be followed by notable advances which in many 
cases are direct results of new discoveries in other depart¬ 
ments. Take, for example, Faraday’s well-known piece of 
apparatus we call the induction coil. After many years 
this attained the type commonly known as the Ruhmkorff 
coil. Thereafter came the invention of practical forms of 
dynamo-electric generators and the widespread application 
of electricity to commercial operations. This opened up a 
new field of growth and by a simple inversion, as it were, of 
the familiar instrument employed up to that time, princi¬ 
pally to illuminate Geisler and Crooks’ tubes, the induction 
coil of the laboratory became the electric welding machine 
15—Bull. Phil. Soc., Wash., Vol. 14. 
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