[October, 
498 On Scientific M ethod . 
established generalisations of science may not have held 
good during all past time. Sir Wm. Thomson has shown 
how to deduce (from Fourier’s “ Theorem of Heat ”) in 
certain cases the thermal state of a body in past time from 
its known condition at present, and one of the results of his 
investigation is the indication of “ A certain date in past 
time such that the present state of things cannot be deduced 
from any distribution of temperature occurring previously to 
that date, and becoming diffused by ordinary conduction. 
Some other event beyond ordinary conduction must have 
occurred since that date in order to produce the present 
state of things. This is only one of the cases in which a 
consideration of the dissipation of energy leads to the deter- 
mination of a superior limit to the antiquity of the observed 
order of things.”* 
It is possible to imagine a law which should exhibit a 
break, or breaks, of continuity. Babbage has shown that it is 
theoretically possible to devise a machine which shall workac- 
cording to a fixed law for any finite period of time, and yet at a 
fixed moment exhibit a single breach of the law. The machine 
might, for instance, be constituted so as to continue counting 
the natural numbers for an immense period of time. “ If 
every letter in the volume now before the reader’s eyes,” says 
Babbage, “were changed into a figure, and if all the figures 
contained in a thousand such volumes were arranged in order, 
the whole together would yet fall far short of the vast induc- 
tion the observer would have had in favour of the truth of 
the law of natural numbers. . . . Yet shall the engine, 
true to the prediction of its inventor, after the lapse of myriads 
of ages, fulfil its task, and give that one, the first and only 
exception, to the time-sanCtioned law. What would have 
been the chances against the appearance of the excepted 
case immediately prior to its occurrence ?”t 
In the application of scientific generalisations we assume 
that the future will be as the present ; we overlook, neces- 
sarily, the chance of sudden interferences with the present 
order of things. Yet we have no ground for denying the 
possibility of such interferences. There are faCts which 
make the existence of numerous dark bodies in space very 
probable. How do we know that by the collision of one of 
these unseen bodies with this planet the present order of 
things may not be suddenly terminated ? Have we invest!- 
* Clerk Maxwell, Theory of Heat, p. 244, 245. 
f Ninth Bridgewater Treatise, p. 140, quoted by Tevons, Principles of 
Science, vol. ii., p. 437. 
