These examples may suffice to impress at once upon theologians and scientists,--and upon the public mind also,--the obvious, but easily forgotten lesson, that there is need for deliberation before we can clearly decide the exact significance of new scientific discoveries. Neither the spirit of religion, nor the scientific spirit, disposes inquirers to make haste. There is a basis of certainty, sufficiently broad and deep to deliver the mind from concern lest intellectual confusion should arise from continued observation and thought. Enthusiasm, acuteness, patience, and also boldness of speculation, are needed in order to widen the range of our knowledge of the mysteries of existence; but caution is as certainly a necessary feature in the gathering of appliances which must lie at the command of theologians and also of scientific observers. In fact, there is at every fresh advance in science, much _thinking_ to be done, after observation and exposition have accomplished their part, and this thinking can not be quickly done. Towards a clear marking out of the boundaries of science and religion, it is needful that some definition or description of both be attempted. It is easy to be religious without sharply marking off for one's self the exact boundaries of religion; and equally easy to be scientific, without exactly laying down the limits of science. But any intelligent view of the relations of the two is not to be had without carefully marking off the territory which they respectively occupy. Science at least should seek for itself "a scientific boundary," and though this is not always easily found, it is essential for keeping up friendly relations with neighboring states. In view, therefore, of the requirements of the present subject, something must here be done in the way of definition, or at least, description, delicate and difficult as is the task.