be proved nor disproved, are the conventional definitions of matter, and accepted distinctions between matter and mind, or other forms of force.
The qualities that for ages have been attributed to matter, as inertia and extension, apply correctly enough to that limited portion and form of matter that the senses can appreciate; but, as has been shown, all but an infinitesimal portion of Nature is permanently sealed against the senses. What warrant have we, beyond undemonstrable probability, that the attributes of that portion of matter that can be reached by the senses belong also to all that portion of which the senses can directly teach us nothing? How do we know that the familiar forces, as light, heat, electricity, and gravity, may not be as truly matter as the Atlantic Ocean or Mont Blanc?
Standing on the outermost verge of conceivable science, and casting the line of probability into the dark unknown, as far as it is possible for human weakness, will it, can it reach any more rational generalization than this, that all Nature is unity? Whether the common axioms of human reasoning—such as the whole is greater than a part, every effect must have an adequate cause, every thought must have a thinker, a thing cannot be and not be at the same time—do or do not apply to the supernatural, the mind of man is powerless to determine.
Under this head come all conceivable questions relating to the existence and nature of other universes than ours.
A question of great interest, or would be if it could be answered, is that of spontaneous generation, which from the limitations of the human senses can neither be proved nor disproved.
How is it possible for the human faculties to determine what degree of heat any supposable living substance, or intermediate substance between living and non-living, beyond the reach of the microscope, may bear? There are gradations of endurance in living things that are accessible to the senses. What are the limits of this gradation through the realm of the infinitely little? If, therefore, all experts in this branch of inquiry should agree that fluids subjected to a very much higher degree of heat than has yet been employed in experiments of this kind shall yet, when every conceivable precaution against sources of error has been taken, develop some of the lower forms of life, the question of spontaneous generation would still be an open one.
The present and prospective state of the spontaneous generation question is, then, as follows:
1. Science has no absolute deduction for or against it.
2. It is impossible by present deduction or by conceivable induction to either positively prove or disprove it.
Discussions on the subject, like that between Tyndall and Bastian, are on both sides unscientific, as they are unsatisfactory, and would not be indulged in by those who have correct ideas of the limitations of the senses.