74. Nevertheless in this triumphal march the progress has always been from the less to the more perfect, from the glimmering of early dawn to the clear morning light, if not to the bright beams of the noon-day sun. Temporary obstacles have appeared only to be surmounted, and like Augustine’s ladder to constitute a platform from which a higher and more comprehensive view might be obtained. Difficulties too, other than physical,—struggles, weariness, opposition—have been encountered and overcome, nor has there been anything like a grave defeat, or the production of permanent confusion. The concluding words of the _Te Deum_ have been abundantly fulfilled in the experience of the astronomer. He has trusted in God, and he has never been confounded. 75. Here then we have an instance of what is meant by Continuity. It does not imply an easy progress, or a smooth level road; it is consistent with a temporary halt, perhaps not even inconsistent with a temporary break-down, or with momentary despair. We are met by difficulties of many kinds—the rock, the tangled growth, the swamp, the thick darkness, but never by the abyss. Nothing has occurred to convince us that our path has been absolutely wrong from the very commencement, and that we must altogether retrace our steps; and the same thing holds in other problems besides those of astronomy. Once we have accumulated sufficient trustworthy evidence to show us that we are in the right way, we are never afterwards irretrievably defeated. Before proceeding further, let us here notice a peculiarity which, if it be clearly exhibited in the progress of astronomy, is yet by no means confined to that science, but appears to be characteristic of all physical knowledge. Things are so arranged and the intellect of man is so constituted that we are led in the progress of science to recognise certain laws which appear at first sight to hold exactly, or which, in other words, have the appearance of absolute truths. As time passes on, and our instruments become more delicate, while our observations with them are multiplied, signs begin to show themselves of very slight deviations from exactitude in these laws.