38 KANSAS CITY REVIEW OF SCIENCE. 
white ball, we would properly decide that white balls are greatly in the majority, 
but we might continue for a century without drawing the single black ball that the 
urn might contain. 
So it is with all human experience in this world. If we could range at will 
through space and time, we might well be surprised, as Tolver Preston has sug- 
gested, by the greatly varying conditions which we might find in other and un- 
known parts. of the all-embracing universe ; just as a minute being, inhabiting for 
a brief moment a single atom of a gas, and who might imagine that he had be- 
come quite familiar with his little world, would find much to learn, could he ex- 
tend his observations over a longer time, or over a wider space. He would then 
find the greatest variety in the motions of neighboring molecules of the gas. 
Some moving with extreme slowness—others with extreme velocity—the same 
differences being observed in the velocities of their rotations. Moreover these 
velocities are being constantly changed, by collision of neighboring molecules— 
collisions which must often result in the separation of the molecules into their 
constituent atoms. 
It may well be, as Preston ingeniously suggests, that all this is repeated on 
an immensely grander scale. Perhaps our solar system is rushing through space, 
with a motion compared with which the relative motions of its various parts are _ 
utterly insignificant. Collisions, instead of happening to each atom many 
millions of times per second, as in the case of gases, are here separated by im- 
mensely long intervals, and it is a minute portion of one of these intervals 
which represents the life-time of our humanity upon one of the atoms of the uni- 
verse. Possibly we are not yet acquainted with the average conditions of the 
universe, our attention being confined, for a comparatively brief interval, to a 
few of the atoms which for the present are nearest to us. 
We are able to predict the probable history of our earth, in the comparatively 
near future, but we know almost nothing of what the remote future may bring. 
Here we have fairly entered the domain of chance, which is the domain of human - 
ignorance. 
It is essential to bear in mind that probability is a thing which belongs, not 
to the events which are probable, but to the mind, depending as stated upon our 
knowledge, or rather upon what we think we know. 
This is clearly shown by the fact that different persons may regard the same 
event with very different degrees of probability ; for example: A thinks he saw 
a ball dropped into a box, and thinks he knows that it is yet there. B is certain 
that it was a juggler’s trick, and that the boxis empty. CC did not see the act and . 
has no opinion in the matter. The conclusions which these men will form will 
depend upon their previous experiences, their opportunities for observation and 
their native ability. Their confidence in their conclusions is not necessarily de- 
pendent upon the real facts. Or, to take another case cited by Jevons: ‘*‘A 
steamer is missing, and certain workmen in a dock-yard, knowing that she is 
poorly built, believe she is lost. The public is informed that she is well built, 
