768 Transactions of the American Institute. 



existence of two sources of strength in the constitution; one is 

 called the force in use, and the other the reserved force. Doubtless 

 the period of decadence bears some relation to the period required 

 for full development. Those who are long in arriving at the full 

 maturity of their powers, as a general rule, are long in losing their 

 store of reserved force. Bodily strength may be compared to a 

 .water-power. During the period of growth, the surplus vitality is 

 used in development, as force is expended in building structures to 

 raise the head and fall of water. Through the term of middle life, 

 the supply of strength greatly exceeds that expended in work, and 

 the surplus quietly passes off like unused water over the waste- 

 weir. When the period of decadence arrives, the stream begins 

 to diminish. There is no longer a residue of unused force. 

 During the day there is no flow of water over the weir, and a 

 whole night is required to bring the head and flow to its accus- 

 tomed height. Eveiy resource for supply is employed, and care 

 is taken to prevent the escape of unused force. Gradually the 

 constitution is enfeebled, but has not even power to repair bodily 

 waste. The weir crumbles, the leakages are no longer checked. 

 Slower and slower turns the wheel of life, mitil at last, by some 

 sudden diversion, its scanty supply is cut ofl^, and it has forever 

 ceased to move. To guard the weir of life, to prevent its sudden 

 destruction by fatal disease, and to show how best to repair the 

 damage of constant decay, is the business of the physician. It is 

 said the average length of human life among civilized nations has 

 been greatly increased during the last century. This gratifying 

 result must be accredited in part to the introduction of new reme- 

 dies for disease; yet it will not be out of place to assert that the 

 most important of all arts — medicine — has not kept pace in 

 improvement with many others aftecting the material well-being 

 of man. 



An animated discussion took place on the item in relation to the 

 cure of disease by the application of cold, in Avhich Dr. H. D. 

 Sheppard and T. D. Stetson, Esq., bore a prominent part. 



ACOUSTICS. 



The Chairman presented the following papers, read at the meet- 

 ing of the Association for the Advancement of Science, held at 

 Burlington, Vermont, in August, 1867: 



