In illustration of this sense of wonder which links together poetry and science, let me allude briefly to a few matters that belong to my own small corner in the great universe of knowledge, that of light invisible and of life unvoiced. Can anything appeal more to the imagination than the fact that we can detect the peculiarities in the internal molecular structure of an opaque body by means of light that is itself invisible? Could anything have been more unexpected than to find that a sphere of China-clay focuses invisible light more perfectly than a sphere of glass focuses the visible; that in fact, the refractive power of this clay to electric radiation is at least as great as that of the most costly diamond to light? From amongst the innumerable octaves of light, there is only one octave, with power to excite the human eye. In reality, we stand, in the midst of a luminous ocean, almost blind! The little that we can see is nothing, compared to the vastness of that which we cannot. But it may be said that out of the very imperfection of his senses man has been able, in science, to build for himself a raft of thought by which to make daring adventure on the great seas of the unknown. UNVOICED LIFE. Again, just as, in following up light from visible to invisible, our range of investigation transcends our physical sight, so also does our power of sympathy become extended, when we pass from the voiced to the unvoiced, in the study of life: Is there then any possible relation between our own life and that of the plant world? That there may be such a relation, some of the foremost of scientific men have denied. So distinguished a leader as the late Burdon-Sanderson declared that the majority of plants were not capable of giving any answer, by either mechanical or electrical excitement, to an outside stock. Pfeffer, again, and his distinguished followers, have insisted that the plants have neither a nervous system, nor anything analogous to the nervous impulse of the animal. According to such a view, that two streams of life, in plant and animal, flow side by side, but under the guidance of different laws. The problems of vegetable life are, it must be said, extremely obscure, and for the penetrating of that darkness we have long had to wait for instruments of a superlative sensitiveness. This has been the principal reason for our long clinging to mere theory, instead of looking for the demonstration of facts. But to learn the truth we have to put aside theories, and rely only on direct experiment. We have to abandon all our preconceptions, and put our questions direct, insisting that the only evidence we can accept is that which bears the plant's own signature.