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peculiar aptitude, which enables him by a peremptory instinct 
to draw conclusions and predicate results which other men 
may be incapable of seeing. I most fully admit the existence 
of peculiar mental aptitudes developed in every branch of con- 
nected and consecutive study, and existing within their respec- 
tive spheres, in the lawyer, the theologian, the preacher, the 
musician, the statesman, the man of letters, as well as in the man 
of science. But I wish to point out that these special apti- 
tudes exist within very strait limits. They have their definite 
sphere beyond which they cannot pass. There is a stage in 
the process of scientific investigation where they cease, and 
the question passes to a broader sphere, where all men have 
equal liberty of entrance ; the moment the investigation has 
reached this stage, the man of science ceases to possess any 
special apparatus, any extensive aptitude, any peculiar instinct, 
any royal road to his conclusion. Not only so, but it may be 
questioned whether he has not special disadvantages, and 
whether the peculiar habitude which was of immense value to 
him up to this point, does not become a positive hindrance 
beyond it. 
Let me rapidly sketch the mental processes involved in 
scientific investigation. First comes the observation of the 
facts ; and for this high and peculiar mental gifts are needed. 
To teach how to observe, and how to observe accurately, is one 
of the prime objects of modern education. The one fact must 
be separated from the thousand other facts among which it is 
embedded. Both incessant practice and a wide reach of 
knowledge, that is of accurate acquaintance with other facts 
previously known, are necessary for this. I have known a 
person accustomed to walk through the country without 
the slightest consciousness of any difference between the 
foliage of one tree or of another, yet that person would have 
detected a false note in music which a less cultivated ear 
would never have noticed. I have often found myself in- 
capable of distinguishing between two ferns of somewhat 
similar appearance, because I have not been familiar with the 
names and exact structure of any one — the difference of one 
stratum from another, or the recognition of anything peculiar 
in the relative position of strata ; the distinction between one 
bone and another of a fossil of an extinct species from another 
fossil of an existing species — are common and familiar in- 
stances where a trained habit of observation immediately and 
confidently perceives what is wholly hid from an eye untrained. 
Some men perhaps would scarcely know what is meant by the 
fact of flint implements being found in drift ; that a certain 
heap of flints have really been fashioned, however rudely, by 
