copper and other substances during rotation, 509 
subject ; and I beg you will make whatever use you think 
proper of them, and likewise of the account I before sent 
you.* 
I am, dear Sir, 
very truly your's, 
S. H. CHRISTIE. 
* In a former letter, dated May 1 1 : the experiments related in which arc embo- 
died in this communication. (H.) 
Royal Military Academy, 
I ztk June, 1 825, 
