ADDRESS OF PROF. A. M. MAYER. 503 



the pile and noticed the amount of deflection produced in the 

 needles of the galvanometer by the thermo-electric current. Then 

 the part? of the sun's image adjacent to the spot were brought to 

 the thermopile; and now he observed a greater deflection in the 

 galvanometer than in the previous experiment ; thus "clearly prov- 

 ing," as he says, "that the spot emitted less heat than the surround- 

 ing parts of the luminous disc." 



This new method of research originated with Henry. It was 

 shown to Secchi while he was in this country as Professor in the 

 College of Georgetown. On his return to Europe Secchi obtained 

 no inconsiderable repute by extending these observations — using 

 the methods of Henry, but, I fear, not giving sufficient credit to 

 the originator of them. But let that pass; for the bread which 

 Henry cast upon the waters has returned to our own shores — thanks 

 to the genius and perseverance of our colleague Langley. 



Most reluctantly do I here desist from citing further the works 

 of Henry. It is impossible to crowd into one brief hour the 

 thoughts which were his occupation during more than half a cen- 

 turv. I have at least endeavored to exhibit before you the more 

 important of the labors of his life. What shall we think of them? 

 Surely they are on as high a plane as those of any of his contem- 

 poraries, and show as much originality as theirs in their conception — 

 as much skiil in their execution. Yet it has been said that Henry 

 was not a man of genius. As I have not been able to find that the 

 philosophers, who have the special charge of giving- from time to 

 time definitions of genius, have been able to come to any satisfactory 

 conclusion among themselves, I will leave their company, and, 

 with your liberty, take my definition from a book which, if we 

 accredit Thackeray, is one of the very best novels ever written 

 in English. After listening to this, you may form your own 

 opinions as to whether Henry did or did not possess genius: "By 

 genius I would understand that power, or rather those powers of 

 the mind which are capable of penetrating into all things within 

 our reach and knowledge, and of distinguishing their essential 

 differences, These are no other than invention and judgment: and 

 they are both called by the collective name of genius, as they are of 

 those gifts of nature which we bring with us into the world. Con- 



