viii INTEODl 



mpted. Among minerals, only those having approxu 

 definite formula are given, and indefinite Bubstancea haw iluded 



altogether. The tables aim at reasonable compl 



Htution, and all else is gratuitous. A 

 many determination* gravity haw been unearthed from doctoral 



diss* r; shool programmes, and similar foes of the bibliographer, and 



doubtless other data so printed have escaped my notice altogether. There 

 is a weakness of human nature which, masqueradi tism, some- 



n of science to bury valuable researi scure local pub- 



08, and a compiler may never datter himself that no such paper has 

 1 his vigilance. I -hall be glad to receive notice of all omissions, and 

 will try to rectify Buch or other errors in future supplements or app udices. 

 A word in conclusion as to the extent of the table. They contain the 

 specific gravities of 5,227 distinct substances ami 1.4,465 separate determi- 

 nations. The original edition gave only 2,263 Bubstances, to which nearly 

 700 were added in the supplement The increae irthy indication 



of existing chemical activity. 



F. W. CLAKKi:. 

 Washington, June 20, 1888. 



