2 INTRODUCTION. 



is immediately transmitted to the farthest limits of the system, 

 in oscillations which correspond in their periods with the cause 

 producing them, like sympathetic notes in music, or vihrations 

 from the deep tones of an organ. 



The heavens afford the most sublime subject of study which 

 can be derived from science. The magnitude and splendour of 

 the objects, the inconceivable rapidity with which they move, 

 and the enormous distances between them, impress the mind with 

 some notion of the energy that maintains them in their motions, 

 with a durability to which we can see no limit. Equally con- 

 spicuous is the goodness of the great First Cause, in having 

 endowed man with faculties, by which he can not only appreciate 

 the magnificence of His works, but trace, with precision, the 

 operation of His laws, use the globe he inhabits as a base where- 

 with to measure the magnitude and distance of the sun and 

 planets, and make the diameter (Note 1) of the earth's orbit the 

 first step of a scale by which he may ascend to the starry firma- 

 ment. Such pursuits, while they ennoble the mind, at the same 

 time inculcate humility, by showing that there is a barrier which 

 no energy, mental or physical, can ever enable us to pass : that, 

 however profoundly we may penetrate the depths of space, there 

 still remain innumerable systems, compared with which, those 

 apparently so vast must dwindle into insignificance, or even 

 become invisible ; and that not only man, but the globe he in- 

 habits nay, the whole system of which it forms so small a part 

 might be annihilated, and its extinction be unperceived in the 

 immensity of creation. 



A complete acquaintance with physical astronomy can be at- 

 tained by those only who are well versed in the higher branches 

 of mathematical and mechanical science (N. 2), and they alone 

 can appreciate the extreme beauty of the results, and of the 

 means by which these results are obtained. It is nevertheless 

 true, that a sufficient skill in analysis (N. 3) to follow the general 

 outline to see the mutual dependence of the different parts of 

 the system, and to comprehend by what means the most extra- 

 ordinary conclusions have been arrived at, is within the reach 

 of many who shrink from the task, appalled by difficulties, not 

 more formidable than those incident to the study of the elements 

 of every branch of knowledge. There is a wide distinction 

 between the degree of mathematical acquirement necessary for 



