630 
form neither affect our existence nor our welfare; 
and we are not compelled by any physical neces- 
sity to correct them. Imagination, on the con- 
trary, which is ever wandering beyond the bounds 
of truth, joined to self-love and that self-confi- 
dence we are so apt to indulge, prompt us to draw 
conclusions which are not immediately derived from 
facts; so that we become in some measure inter- 
ested in deceiving ourselves. Hence it is by no 
means surprising, that, in the science of physics 
in general, men have so often formed suppositions, 
instead of drawing conclusions. These supposi- 
tions, handed down from one age to another, ac- 
quire additional weight from the authorities by 
which they are supported, till at last they are re- 
‘eeived, even by men of genius, as fundamental 
truths. 
The only method of preventing such errors from 
‘taking place, and of correcting them when 
formed, is to restrain and simplify our reasoning 
as much as possible. This depends entirely on 
ourselves, and the neglect of it is the only source 
of our mistakes. We must trust to nothing but 
facts: These are presented to us by Nature, and 
ean not deceive. We ought, in every instance, to 
submit our reasoning to the test of experiment, 
and never to search fior truth, but by the natural 
road of experiment and observation. 
‘Thoroughly convinced of these truths, I have im- 
posed upon myself, as a law, never to advance but 
from what is known to what is unknown; never to 
form any conclusion which is not an immediate 
consequence necessarily flowing from observation 
and experiment. 
Such, then, were the principles of this great 
master scientist of France as he wrote them 
a hundred and twenty-five years ago. And 
yet they seem vibrant with the teachings of 
our own day and generation. Perhaps it may 
be of imterest to examine the growth of this 
modern mental attitude, especially in its re- 
lation to medicine. 
The universities of Cambridge (founded in 
1229) and Oxford (founded in 1249) were 
established at a time when authority was wor- 
shipped. It was not until after the revival of 
learning in Italy that the original versions 
of the ancient classics of Greece and Rome 
were brought to these English universities, 
there to be studied at first hand and the un- 
known culture of a bygone civilization re- 
vealed. In this way it was learned, for ex- 
SCIENCE 
[N. 8S. Vou. XLVIII. No. 1252 
ample, that Hippocrates (circa B.c. 430) had 
been misquoted by Galen, for the Father of 
_Medicine in truth had remarked: 
Whoever having undertaken to speak and write 
on medicine have first laid down for themselves 
some hypothesis to their argument such as hot or 
cold or moist or dry or whatever else they choose 
(thus reducing their subject within a narrow com- 
pass and supposing only one or two original 
causes of disease or of death among mankind) are 
clearly mistaken in much that they say. 
This was a far more liberal doctrine than 
the interpretation of Galen (+ a.v. 200) who, 
in his medical definitions, says: “The ele- 
ments of medicine, as some of the ancients 
thought, are hot and cold, moist and dry” 
and “ Of what do our material bodies con- 
sist? Of the four elements, fire, air, earth 
and water.” 
So from this ancient fount of information 
Chaucer’s doctor knew the causes of diseases: 
He knew the cause of every malady 
Were it of cold or hot or moist or dry 
And where engendered and of what humour, 
He was a very perfect practisour. 
It is evident that the revival of learning in 
the fifteenth and sixteenth centuries, with its 
scholarly search through the buried classics, 
must have had a profound influence upon 
men’s minds in its revelation of the forgotten 
past. That the elements of Empedocles, fire, 
air, earth and water, should have been the 
accepted basis of the chemical world for 
nearly two thousand years seems incredible to 
the modern mind. And yet, when one con- 
siders the past, one is forced to the conviction 
that the general adoption of revolutionary 
principles, as lately carried out in Russia, 
might once again reduce the world to the 
condition in which it existed during the Dark 
Ages. And one might conceive that a Eu- 
ropean or an American a hundred years hence 
might have to travel to Tokio in order to find 
a copy of the Journal of Biological Chemistry. 
Galileo was born in 1564 and was the first 
great modern scientist who chose to trust his 
own observations rather than accept the teach- 
ings of authorities. In 1633 he was forced by 
