388 SCIENCE. 
the reaction of language on thought is so 
subtle and far-reaching that, risking the ac- 
cusation of pedantry, I would urge the 
abolition of all such picturesque terms. In 
our quantitative estimates let us be content 
with ‘high’ or ‘low,’ ‘great’ or ‘small,’ 
and let us remember that there is no such 
thing as a failure to obey a physical law. 
A broken law is merely a false description. 
Concurrently with the change in our con- 
ception of physical law has come a change 
in our conception of physical explanation. 
We have not to go very far back to find 
such a statement as this—that we have ex- 
plained anything when we know the cause 
of it, or when we have found out the reason 
why—a statement which is only appropriate 
on the psychical view. Without entering 
into any discussion of the meaning of cause, 
we can at least assert that that meaning will 
only have true content when it is concerned 
with purpose and will. On the purely 
physical or descriptive view, the idea of 
cause is quite out of place. In description 
we are solely concerned with the ‘how’ of 
things, and their ‘why’ we purposely leave 
out of account. We explain an event not 
when we know ‘why’ it happened, but 
when we show ‘how’ it is like something 
else happening elsewhere or otherwhen— 
when, in fact, we can include it as a case 
described by some law already set forth. 
In explanation, we do not account for the 
the event, but we improve our account of 
it by likening it to what we already knew. 
For instance, Newton explained the fall- 
ing of a stone when he showed that its ac- 
celeration towards the earth was similar to 
and could be expressed by the same law as 
the acceleration of the moon towards the 
earth. 
He explained the air disturbance we call 
‘sound’ when he showed that the motions 
and forces in the pressure waves were like 
motions and forces already studied. 
Franklin explained lightning when and 
[N.S. Von. X. No. 247. 
so far as he showed that it was similar in 
its behavior to other electric discharges. 
Here I do not fear any accusation of ped- 
antry in joining those who urge that we 
should adapt our language to the modern 
view. It would be a very real gain, a great 
assistance to clear thinking, if we could en- 
tirely abolish the word ‘ cause’ in physical 
description, cease to say ‘ why’ things hap- 
pen unless we wish to signify an antecedent 
purpose, and be content to own that our 
laws are but expressions of ‘how’ they 
oceur. 
The aim of explanation, then, is to reduce 
the number of laws as far as possible, by 
showing that laws, at first separated, may 
be merged in one; to reduce the number 
of chapters in the book of science by show- 
ing that some are truly mere sub-sections 
of chapters already written. 
To take an old but never-worn-out meta- 
phor, the physicist is examining the garment 
of Nature, learning of how many, or rather 
of how few different kinds of thread it is 
woven, finding how each separate thread 
enters into the pattern, and seeking from 
the pattern woven in the past to know the 
pattern yet to come. 
How many different kinds of thread does 
Nature use ? 
So far, we have recognized some eight or 
nine, the number of different forms of 
energy which we are still obliged to count 
as distinct. But this distinction we cannot 
believe to.be real. The relations between 
the different forms of energy, and the fixed 
rate of exchange when one form gives place 
to another, encourage us to suppose that 
if we could only sharpen our senses, or 
change our point of view, we could effect a 
still further reduction. We stand in front 
of Nature’s loom as we we watch the weay- 
ing of the garment; while we follow a par- 
ticular thread in the pattern it suddenly 
disappears, and a thread of another color 
takes its place. .Is this a new thread, or is 
