DECEMBER 8, 1899. ] 
In time we are limited by a few hundred 
or possibly thousand years: indeed the 
limit in our science is far less than the 
smaller of these periods. In space we have 
exact knowledge limited to portions of our 
earth’s surface and a mile or so below the 
surface, together with what little we can 
learn from looking through powerful tele- 
scopes into the space beyond. In tempera- 
ture our knowledge extends from near the 
absolute zero to that of the sun but exact 
knowledge is far more limited. In pres- 
sures we go from the Crookes vacuum still 
containing myriads of flying atoms to pres- 
sures limited by the strength of steel but 
still very minute compared with the pres- 
sures at the center of the earth and sun, 
where the hardest steel would flow like the 
most limpid water. In velocities we are 
limited to a few miles per second. In forces 
to possibly 100 tons to the square inch. In 
mechanical rotations to a few hundred 
times per second. 
All the facts which we have considered, 
the liability to error in whatever direction 
we go, the infirmity of our minds in their 
reasoning power, the fallibility of witnesses 
and experimenters, lead the scientist to be 
specially sceptical with reference to any 
statement made to him or any so-called 
knowledge which may be brought to his at- 
tention. The facts and theories of our sci- 
ence are so much more certain than those 
of history, of the testimony of ordinary 
people on which the facts of ordinary his- 
tory or of legal evidence rest, or of the 
value of medicines to which we trust when 
we are ill, indeed to the whole fabric of sup- 
posed truth by which an ordinary person 
guides his belief and the actions of his life, 
that it may seem ominous and strange if 
what I have said of the imperfections of the 
knowledge of physics is correct. How 
shall we regulate our minds with respect to 
it: there is only one way that I know of 
and that is to avoid the discontinuity of the 
SCIENCE 
831 
ordinary, indeed the so-called cultivated 
legal mind. There is no such thing as ab- 
solute truth and absolute falsehood. The 
scientific mind should never recognize the 
perfect truth or the perfect falsehood of any 
supposed theory or observation. It should 
carefully weigh the chances of truth and 
error and grade each in its proper position 
along the line joining absolute truth and 
absolute error. 
The ordinary crude mind has only two 
compartments, one for truth and one for 
error ; indeed the contents of the two com- 
partments are sadly mixed in most cases : 
the ideal scientific mind, however, has an 
infinite number. Each theory or law is in 
its proper compartment indicating the prob- 
ability of its truth. As a new fact arrives 
the scientist changes it from one compart- 
ment to another so as, if possible, to always 
keep it in its proper relation to truth and 
error. Thus the fluid nature of electricity 
was once in a compartment near the truth. 
Faraday’s and Maxwell’s researches have 
now caused us to move it to a compart- 
ment nearly up to that of absolute error. 
So the law of gravitation within plane- 
tary distances is far toward absolute truth, 
but may still need amending before it is 
advanced farther in that direction. 
The ideal scientific mind, therefore, must 
always be held in a state of balance which 
the slightest new evidence may change in 
one direction or another. It is in a con- 
stant state of skepticism, knowing full well 
that nothing is certain. It is above all an 
agnostic with respect to all facts and the- 
ories of science as well as to all other so- 
called beliefs and theories. 
Yet it would be folly to reason from this 
that we need not guide our life according 
to the approach to knowledge that we pos- 
sess. Nature is inexorable; it punishes the 
child who unknowingly steps off a precipice 
quite as severely as the grown scientist who 
steps over, with full knowledge of all the 
