ADVERTISEMENT. 



The Smithsonian Institution has long had in contemplation the pul pli- 

 cation of a series of " Constants of Nature," and has accepted the fol- 

 lowing work as the first part of such a series. Other parts will be pub- 

 lished in succession as soon as the matter for them may be obtained 

 and the finances of the Institution will warrant. 



The present work was referred for critical examination to Professors 

 Joy and Chandler of Columbia College, New York, and has been pub- 

 lished on their recommendation. 



JOSEPH HENRY, 



Secretary S. I. 



Washington, D. C, December, 1873. 



ELECTROTTPED BY 

 MACEELLAR, SMITHS, i JORDAN, PHILADELPHIA. 



COLLINS, PRINTER. 



