knowledge of every theoretical and instrumental detail can only be obtained by those who will devote to them a large portion of their lives; but sound knowledge of the principles of nearly every part, can be obtained by the reasonable efforts of persons possessing common opportunities for general knowledge.
The second conclusion, however, is that, easy of comprehension as are the successive steps of Astronomical investigation, the united succession of all is not to be seized lightly. Let no one think that the problem, for instance, of the measure of the Earth's distance from the Sun is to be mastered by one reading. Again and again must the student return to it; again and again must he doubt and become convinced; again and again must he trace his own diagrams, and express the reasoning in his own language, before all the troubles (I will not call them difficulties) are overcome. And perhaps one of the most valuable results to be derived from a truly intellectual study of Astronomy is, the habit of keeping up a sustained attention to all the successive steps of a long series of reasonings. Power, and with it dignity, are gained to the mind by this noble exercise.
To those who will venture upon the study of the science in this connected way, I can promise an ample and immediate reward. It is not simply that a clear understanding is acquired of the movements of the great bodies which we regard as the system of the world, but it is that we are introduced to a perception of laws governing the motion of all matter, from the finest particle of dust to the largest planet or sun, with a degree of uniformity and constancy, which otherwise we could hardly have
