466 MEMORIAL OF JOSEPH HENRY. 



would be produced by a difference in the motions of two contiguous 

 bodies of air, whether the line of change was vertical or horizontal. 

 As we know very well that the motion, of the air is by no means 

 uniform, and that eddies, gusts, and whiifs prevail nearly every- 

 where, it is to be expected that sound will not always move uni- 

 formly in a direct line, but will be turned from its direct course by 

 the sort of refraction that we have described. It is however im- 

 possible to prove by observation that this is the only cause of the 

 abnormal phenomena referred to, because the exact velocity of local 

 currents within a space over which the sound extends cannot be a 

 subject of observation. Professor Henry was however disposed 

 to claim that, having a sufficiently general known cause to account 

 for the phenomena, it was not philosophical to assume other causes 

 in the absence of decisive proof. 



It was at the light-house station in the month of December, 

 1877, that Professor Henry noticed the first symptom of the 

 disease which terminated his life a few months later. After passing 

 a restless and uncomfortable night, he arose in the morning, finding 

 his hand partially paralyzed. A neighboring physician, being sent 

 for, gave a prognosis of a very serious character. A more detailed 

 subsequent examination by two members of our Academy led to the 

 conclusion that he was affected with an incipient nephritis. Although 

 no prospect of recovery could be held out, it was hoped that the 

 progress of the disease would be so slow that, with his healthy con- 

 stitution, he might still endure for a considerable period. This 

 hope however rapidly faded. During the winter the disease 

 assumed so decided a form as to show that his active work was done 

 and that we could have him with us but a few months longer. But 

 beyond a cessation of his active administrative duties there was no 

 change in his daily life. He received his friends, discussed scientific 

 matters, and took the most active interest in the affairs of the world 

 so long as his strength held out. It was a source of great consola- 

 tion to his family and friends that his intellect was not clouded nor 

 his nervous system shattered by the disease. One of the impressive 

 recollections of the writer's life is that of an interview with him the 

 day before his death, when he was sustained only by the most pow- 

 erful restoratives. He was at first in a state of slumber, but, on 



