COMMISSION 



TO WHICH THIS PAPER HAS BEEN REFERRED. 



Prof. A. E. Church, 

 Prof. L. R. Gibbbs. 



The Smithsonian Institution is under special obligations to the above-named gentlemen, for 

 assistance, in the absence of the author, in revising this paper, and carrying it through the 

 press. 



Joseph Henry, 



Secretary S. I. 



1. K. AND P. O. COLLINS, PE1MTEKS, 

 PHILADELPHIA. 



