Notwithstanding the boasted mathematical precision of the inductive method, and the rigid exactness of its results, scientific men are not wholly exempt from the common infirmity of hasty generalization. They are perpetually liable to the temptation to draw immense conclusions from premises that are too narrow and inadequate. The history of science is a record of the correction of hasty generalizations by future discoveries, and leads to the final conviction that there are no laws of nature which can lay claim to absolute universality. Since the time of Newton, the law of gravitation has been regarded by many as strictly universal. But now we are told by Herschel that "our evidence of the existence of gravitation fails us beyond the region of the double stars, or leaves us at best only a _presumption_ amounting to moral conviction in its favor." Furthermore, in regard to the luminiferous ether, he tells us that "we are freed from the necessity of any mental reference to the actual weight or specific gravity of the material, which in this case is the more necessary, as, though we suppose the ethereal molecules to possess inertia, _we can not suppose them affected by the force of gravitation_." "Beyond all doubt, the widest and most interesting prospect of future discovery ... is that distinction between _gravitating_ and _levitating_ matter, that positive and unrefutable demonstration of the existence of a repulsive force ... enormously more powerful than the attractive force of gravity."[239] Until recently the presence of free oxygen as the necessary condition of life has been regarded as a universal biological law. "But the latest researches of Pasteur have shown that, so far from oxygen being essential to the life of the simplest living beings, there are certain forms of infusoria which not only pass their lives without oxygen, but are killed by its presence."[240]