SCEPTICISM OF THE INSTRUMENT
individuals which is separable from other biological species only by the fact that an enormous number of other linking individuals are inaccessible in time—are in other words dead and gone—and each new individual in that species does, in the distinction of its own individuality, break away in however infinitesimal degree from the previous average properties of the species. There is no property of any species, even the properties that constitute the specific definition, that is not a matter of more or less. If, for example, a species be distinguished by a single large red spot on the back, you will find if you go over a great number of specimens that red spot shrinking here to nothing, expanding there to a more general redness, weakening to pink, deepening to russet and brown, shading into crimson, and so on, and so on. And this is true not only of biological species. It is true of the mineral specimens constituting a mineral species; and I remember as a constant refrain in the lectures of Prof. Judd upon rock classification, the words "they pass into one another by insensible gradations." That is true, I hold, of all things.
You will think perhaps of atoms of the elements as instances of identically similar things, but these are things not of experience but of theory, and there is not a phenomenon in chemistry that is not equally well explained on the supposition that it is merely the immense quantities of atoms necessarily taken in any experiment that mask by the operation of the law of averages the fact that each atom also has its unique quality, its special individual difference. This idea of uniqueness in all individuals is not only true of the
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