PREFACE. 5 



in which constants varying considerably from those now 

 received were assumed. I have further reduced the deter- 

 minations originally given in terms of O = 100, or of O = 

 15.96, to = 16. 'No confusion, however, will be found 

 between the numbers for which the original investigators 

 are responsible and my own. All values which I have cal- 

 culated are in italics, or, with my explanations, enclosed in 

 square brackets. The only arithmetical operation I have 

 permitted myself to perform without these indications is a 

 multiplication or division by two ; and even in such cases 

 it will usually appear from the digest itself that this opera- 

 tion has been performed. 



The abbreviations of the literary references are essentially 

 those adopted in the Royal Society's Catalogue of Scientific 

 Papers. The first reference in each case is to the source 

 upon which I have depended. "When two references are 

 necessary, they are connected by the word and. When my 

 authority is not the original source, that to which it is ac- 

 credited in my authority is also mentioned. 



In conclusion, I shall be grateful to any one who, by 

 drawing my attention to omissions or mistakes, will assist 

 me in perfecting a labor which has occupied all my availa- 

 ble time for twenty months. 



Berkeley, Cal., April, 1878. 



Postscript. 



In preparing the following paper, I designed making it 

 preliminary to a discussion of the various determinations 

 and of the value to be assigned to each, and in this work I 

 had already made some progress. After presenting this 

 paper to the Institution, however, I learned that Prof. F. W. 

 Clarke had been for some time engaged on a similar under- 

 taking, and to him I gladly resigned the discussion of the 

 data here compiled. The two papers will appear in the 

 same form, and may be regarded as complementary. 



G. F. B. 



