TRANSACTIONS OF SECTION A. 583 



Department II. — General Physics. 



1. A71 Apparatus for Verifying the Law of Conservation of Energy in the 

 Human Body. By Professor W. O. Atwater and Professor E. B. 

 EosA. 



The authors undertook their investigation at the Wesleyan University in 1892, 

 under the patronage of the University and the Storrs Experiment Station of Con- 

 necticut. In 1894 the United States Department of Agriculture inaugurated an 

 investigation of the foods and nutrition of the people of the United States, and 

 appropriated some funds for the research. The investigation has been continued 

 for five years, during which time the apparatus has been gradually developed to a 

 comparatively high degree of perfection. 



The general plan of the work is to determine the potential energy of the food 

 «aten by the person under investigation, by burning samples in a bomb calorimeter ; 

 to analyse other samples and determine the chemical composition of the food ; to 

 analyse and burn samples of the waste products of the body ; to measure the 

 heat evolved by the subject and the mechanical work done ; then to balance the 

 total net energy taken into the body against the energy given off as heat and 

 work. _ .... 



The heat was measured by placing the person under investigation m a large 

 calorimeter, especially designed and constructed for this work, where he was her- 

 metically sealed, and where he lived for periods of from one to twelve days. The 

 calorimeter was 7 feet long, 6 feet 4 inches high, and 4 feet wide. Its walls were 

 double and made of sheet copper and sheet zinc, and this chamber was enclosed 

 in concentric wooden walls, to shield the calorimeter from change in temperature 

 vrithout. 



The two metal walls were maintained at exactly the same temperature, so 

 that no heat was gained or lost through the walls, and the heat generated 

 within was carried away by a stream of water flowing through a copper pipe, 

 called an ' absorber.' Tests of the calorimeter were made by passing an electric 

 current through a known resistance, and measuring the heat generated ; and also 

 bv burning alcohol in a lamp and calculating, from the amount of alcohol burned, 

 its composition, and the heat of combustion of pure alcoliol determined by the 

 bomb calorimeter, the amount of heat that should be given, and measuring the 

 heat actually evolved by the respiration calorimeter. These tests showed that 

 the calorimeter is a very accurate instrument. 



This investigation is followed up with studies in the metabolism of matter and 

 energy in the human body. 



2. The Bate of the Decrease of the Intensify of Shrill Sonnds with Time. 

 By A. WiLMER Duff, Purdue University, Indiana. 



Stokes has investigated theoretically the effect of viscosity in dissipating the 

 energy of vibration of shrill sounds, and also, in another paper, the effect of radia- 

 tion Rayleigh has extended his method to thermal conduction, and Kirchhoff 

 has investigated the effect of both viscosity and conduction, arriving at results in 

 agreement with the investigations of Stokes and Ilayleigh, In the present Paper 

 the question is for the first itime approached experimentally. 



The distance at which eight very shrill whistles sounded simultaneously under 

 a definite pressure just become inaudible is observed, and also the distances at 

 which they become inaudible when sounded in pairs. From these observations 

 the modulus of decay of amplitude is found, and for the case of a note of vibration 

 frequency of 10,600 the modulus of decay turns out to be -66. Comparing this 

 result with the theoretical investigations, the effect of radiation only is deduced, 

 and hence a value of -1485 is found for the constant in Newton's lawof cooling in 

 the case of air. These seem to be the only values ever found experimentally for 

 the modulus of decay and for the Newtonian constant of radiation. 



