410 
compound until he has examined carefully whether it possesses 
all the properties which are known to belong to the substance in 
question. And many a time is his caution rewarded by the 
discovery of some distinct difference of melting-point, or of 
crystalline form, &c., which proves that he has made a new 
compound isomeric with the one which he expected to make. 
It seemed probable, from the agreement of the two substances 
in many particulars, that they might be found to agree in all, 
and might be considered to be the same compound ; but com- 
plete proof of that conclusion consists in showing that the new 
substance agrees with all that we know of the old one. 
In the most various ways chemists seek to extend their know- 
ledge of the uniformity of nature ; and their reasonings by ana- 
logy from particulars to particulars suggest the working hypo- 
theses which lead to new observations. Before, however, 
proceeding to test the truth of his hypothesis by experiment, the 
chemist passes in review, as well as he can, all the general know- 
lec ge which has any bearing on it, in order to find agreement or 
disagreement between his hypothesis and the ideas established 
by past experience. Sometimes he sees that his hypothesis is at 
variance with some general law in which he has full confidence, 
and he throws it aside as disproved by that law. On other 
occasions he finds that it follows of necessity from some known 
law, and he then proceeds to verify it by experiment, with a con- 
fident anticipation of the result. In many cases the hypothesis 
does not present sufficiently distinct agreement or disagreement 
with the idcas established by previous investigations to justify 
either the rejection of it or a confident belief in its truth ; for it 
of:en happens that the results of experience of similar pheno- 
mena are not embodied in a sufficiently definite or trustworthy 
statement to have any other effect than that of giving proba- 
bility or the contrary to the hypothesis. 
Another habit of mind which is indispensable for success in 
experimental chemistry, and which is taught by the practice of its 
various operations, is that of truthfulness. 
The very object of all our endeavours is to get true ideas of 
the natural processes of chemical action; for in proportion as 
our ideas are true do they give us the pewer of directing these 
yrocesses. In fact, our ideas are useful only so far as they are 
tiue ; and he must indeed be blind to interest and to duty who 
could wish to swerve from the path of truth. But if anyone 
_were weak enough to make the attempt, he would find his way 
b.rred by innomerable obstacles. 
I-very addition to our science is a matter of immediate interest 
and importance to those who are working in the same direction. 
‘They verify in various ways the statements of the first discoverer, 
and seldom fail to notice further particulars, and to correct any 
little crrors of detail into which he may have fallen. They soon 
make it a stepping-stone to further discoveries. Anything like 
wilful misrepresentation is inevitably detected and made known. 
It must not, however, be supposed that the investigator drifts 
unconsciously into the habit of truthfulness for want of tempta- 
tion to be untruthful, or even that error presents itself to his 
mind in a grotesque and repulsive garb, so as to enlist from the 
first his feelings against it; for I can assure you that the precise 
contrary of these things happens. Error comes before him 
usually in the very garb of truth, and his utmost skill and atten- 
tion are needed to decide whether or not it is entitled,to retain 
that garb. 
You will easily see how this happens if you reflect that each 
woiking hypothesis employed by an investigator is an unproven 
proposition, which bears such resemblance to truth as to give 
rise to hopes that it may really be true. The investigator trusts 
it provisionally to the extent of trying one or more experiments, 
of which it claims to predict the specific result, Even though 
it guide him correctly for a while, he considers it still on trial 
vuril it has been tested by every process which ingenuity can 
su. cest for the purpose of detecting a fault. 
Most errors which an experimentalist has to do with are really 
iuperfect truths, which have done good service in their time by 
guid ng the course of discovery. The great object of scientific 
wotk is to replace these imperfect truths by more exact and 
cc mprehensive statements of the order of nature. 
\.hoever has once got knowledge from Nature herself by 
truful reasoning and experiment, must be dull indeed if he 
Coes not feel that he has acquired a new and noble power, and 
it he does not long to exercise it further, and make new con- 
quests from the realm of darkness by the aid of known truths. 
The habit of systematically searching for truth by the aid of 
known truths, and of testing the validity of each step by con- 
NATURE 
| Sepz. 18, 1873 
stant reference to Nature, has now been practised for a saffi- 
ciently long time to enable us to judge of some of its results. 
Every true idea of the order of Nature is an instrument of 
thought. It can only be obtained by truthful investigation ; and 
itcan only be used effectively in ubedience to the same laws. 
But the first idea which is formed of anything occurring in nature 
affords only a partial representation of the actual reality, by re- 
cording what is seen of it from a particular point of view. By 
examiuing a thing from different points of view we get different 
ideas of -it; and when we compare these ideas accurately with 
one another, recollecting how each one was obtained, we find 
that they really supplement each other. 
We try to form in our minds a distinct image of a thing capa- 
ble of producing these various appearances ; and when we have 
succeeded in doing so, we look at it from the different points of 
view from which the natural object has been examined, and find 
that the ideas so obtained meet at the central image. It usually 
happens that an accurate examination of the mutual bearings of — 
these ideas on a central image suggests additions to them and 
correction of some particulars in them. 
Thus it is that true ideas of a natural phenomenon confirm 
and strengthen one another ; and he who aids directly the deve- 
lopment of one of them is sure to promote indirectly the con- 
solidation of others. 
Each onward step in the search for truth has made us stronger 
for the work ; and when we look back upon what has been done 
by the efforts of so many workers simply but steadily directed by 
truth towards further truth, we see that they have achieved, for 
the benefit of the human race, the conquest of a systematic body 
of truths which encourages men to similar efforts while affording 
them the most effectual aid and guidance. e 
This lesson of the inherent vitality of truth, which is taught 
us so clearly by the history Of our science, is well worthy of the 
consideration of those who, seeing that iniquity and falsehood so 
frequently triumph for a while in the struggle for existence, are 
inclined to take a desponding view of human affairs, and almost 
to despair of the ultimate predominance of truth and goodness. 
I believe it would be impossible at the present time to form an 
adequate idea of the vast consequences which will follow from 
the national adoption of systematic measures for allowing our. — 
knowledge of truth to develop itself freely, through the labours — 
of those who are willing and able to devote themselves to its ser- 
vice, so as to strengthen more and more the belief and trust of 
mankind in its guidance, in small matters as wellas in the highest 
and most important considerations. 
I am desirous of describing briefly the more important of 
those measures ; but first let me mention another habit of mind 
which naturally follows from: the effective pursuit of truth—a 
habit which might be described in general terms as the applica- 
tion to other matters of the truthfulness imparted by science. 
The words which the great German poet put into the mouth 
of Mephistopheles when describing himself to Faust afford per- 
haps the most concise and forcible statement of what we may call 
the anti-scientific spirit :— 
Ich bin der Geist der stets verneint, 
Dem alles, was entsteht, zuwider ist. 
The true spirit of science is certainly affirmative, not negative ; 
for, as I mentioned just now, its history teaches us that the de- 
velopment of our knowledge usually takes place through two or 
more simultaneous ideas of the same phenomenon, quite 
different from one another, both of which ultimately prove to 
be parts of some more general truth; so that a confident belief 
in one of those ideas dues not involve or justify a denial of the’ 
others. 
I could give you many remarkable illustrations of this law 
from among ideas familiar to chemists. But I want you to con- 
sider with me its bearing on the habit of mind called toleration, 
of which the development in modern times is perhaps one of the 
most hopeful indications of moral improvement in man. 
In working at our science we simply try to find out what is 
true ; for although no usefulness is to be found at first in most of 
our results, we know well that every extension of our knowiedge 
of truth is sure to prove useful in manifold ways. So regular an 
attendant is usefulness upon truth in our work, that we get ac- 
customed to expect them always to go together, and to believe 
that there must be some amount of truth wherever there is mani- 
fest usefulness. 
The history of human ideas, so far as it is written in the re- 
cords of the progress of science, abounds with instances of men 
contributing powerfully to the development of important general 
