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question was first put to mechanics. If a positive answer was indicated 
the question was put to nature and the research went on. If the equations 
indicated a negative result the question was dropped and the research 
abandoned. 
Physics was an exact science. Other sciences were not exact sciences 
because their theories and hypotheses could not be mathematically ex- 
pressed—the relation between cause and effect was not expressible in 
algebraical symbols. Physics was an exact science whose fundamental 
principles had been discovered and its laws expressed by equations. All 
that remained to be done was to make more accurate measurements of 
physical quantities for use as coefficients and exponents. 
Let me quote from the 1894 catalogue and later catalogues of one of 
the largest universities in the United States. 
“While it is never safe to affirm that the future of physical science 
has no marvels in stere. * * * it seems probable that most of the grand 
underlying principles have been firmly established and that further ad- 
vances are to be sought chiefly in the rigorous application of these princi- 
ples to all the phenomena which come under our notice. * * * An 
eminent scientist has remarked that the future truths of physical science 
are to be looked for in the sixth place of decimals.” The foregoing is a 
verbatim quotation from the introductory statement preceding the list 
of courses in physics offered at one of our great universities, written, I 
think, in 1894. “Underlying principles firmly established,” “Future truths 
in sixth decimal place,’ 1894. Then came the discovery of Roentgen rays, 
1895; Becquerel rays, 1896; Zeeman effect, 1896; radium, 1898; atomic 
disintegration, the transformation of matter, the thermal effect of radio- 
activity, and intra atomic energy, 1903. I am unable to locate the sixth 
decimal idea in recent catalogues. 
J. J. Thomson likens the discovery of Roentgen rays to the discovery 
of gold in a sparsely populated country. Workers come in large numbers 
to seek the gold, many of them finding that “the country has other products, 
other charms, perhaps even more valuable than the gold itself.” 
The chief value of Roentgen’s discovery was not that it furnished us 
a new kind of light for the investigation of dark places, but in the fact 
that it led a host of workers to study vacuum tube discharges—the dis- 
charge of electricity in gases and the effects of such discharges on matter 
itself. The old dusty Crookes’ tube was taken down from the far corner 
