the late Mr. Henry. S 



only in connexion witli philosophical inquiries. Dr. Black, in 

 an essay which is still, perhaps, not surpassed in chemical phi- 

 losophy as an example of inductive investigation, had fully esta- 

 blished the differences between magnesia in its common and in 

 its calcined state ; but he does not appear to have made trial 

 of the pure earth as a medicine, though several inconveniences 

 from its use in the common form, had long before been pointed 

 out by Hoffman*. On this subject Mr. Henry's claims extend 

 to the free disclosure of his improvements ; to the early and 

 strenuous recommendation of the medicinal use of pure magne- 

 sia ; and to the discovery of some of its chemical agencies. It 

 is but justice to him to state that his recommendation of its em- 

 ployment as a medicine was perfectly disinterested ; for it was 

 not till his work was printed, and on the eve of issuing from the 

 press, that the preparation of magnesia for sale was suggested to 

 him by a friend, in a letter relating to the intended publication, 

 which is still preserved as a part of his correspondence. Before 

 carrying this suggestion into effect, he thought it proper to con- 

 sult Sir John Pringle, Sir Clifton Wintringham, Dr. Warren, 

 and some other leading members of the College of Physicians 

 as to their opinion of the propriety of the measure ; and he did 

 not adopt it until those gentlemen had each declared it to be. 

 not more advisable on his own account, than on that of the 

 public. 



Soon after the publication of the small volume of essays, Mr, 

 Henry found himself involved in a controversy, arising out of 

 some remarks in the appendix, respecting which, as the subject 

 was of temporary interest, it is unnecessary to enter into par- 

 ticulars. It is sufficient to state that the accuracy of some of 

 his experiments, which had been called in question, was con- 

 firmed by the concurrent testimony of Dr. Percival and Dr_ 

 Aikin ; and that the chemical properties, first ascertained by 

 him to belong to pure magnesia, wete considered, by Bergman 

 and by Macquer, as worthy of being incorporated into their 

 rfspeclive histories of that earth. 



• HoHinaii. C)ppr 'I'oni. ■!. p. 381. 



