ASTRONOMY 



PREFACE. 



rilHIS book may be regarded as a second edition of a &quot; Treatise 

 -- on the Mathematical Theory of the Motion of Fluids,&quot; 

 published in 1879, but the additions and alterations are so ex 

 tensive that it has been thought proper to make a change in the 

 title. 



I have attempted to frame a connected account of the principal 

 theorems and methods of the science, and of such of the more 

 important applications as admit of being presented within a 

 moderate compass. It is hoped that all investigations of funda 

 mental importance will be found to have been given with sufficient 

 detail, but in matters of secondary or illustrative interest I have 

 often condensed the argument, or merely stated results, leaving 

 the full working out to the reader. 



In making a selection of the subjects to be treated I have 

 been guided by considerations of physical interest. Long analytical 

 investigations, leading to results which cannot be interpreted, 

 have as far as possible been avoided. Considerable but, it 

 is hoped, not excessive space has been devoted to the theory of 

 waves of various kinds, and to the subject of viscosity. On the 

 other hand, some readers may be disappointed to find that the 

 theory of isolated vortices is still given much in the form in which 

 it was. left by the earlier researches of von Helrnholtz and Lord 

 Kelvin, and that little reference is made to the subsequent 

 investigations of J. J. Thomson, W. M. Hicks, and others, in this 

 field. The omission has been made with reluctance, and can be 

 justified only on the ground that the investigations in question 

 L. b 



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