2 INTRODUCTION. 



to the farthest limits of the system, in oscillations, which cor- 

 respond in their periods with the cause producing them, like 

 sympathetic notes in music, or vibrations 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 conspicuous 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 wherewith 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 firmament. 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 inhabits nay, the whole 

 system of which it forms so small a part might be anni- 

 hilated, and its extinction be unperceived in the immensity of 

 creation. 



A complete acquaintance with physical astronomy can be 

 attained 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 



