34 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



(one vertical divisiou = ^^kVo^ I). Every curve correspoufls to a par- 

 ticular value of c, and the values represented are 1, i, \, 0, — i —A —1 

 respectively. All the curves have, of course, the common asymptote, 

 y = kVq^ I— K, where K is the final rate of flow. 



If Vo is to be 100° C, and the slab is to be originally at room temper- 

 atures, we may put c = J . The ordiuates of the curves in Figure 4 

 represent the flow of heat, when c — J, across the hot face, the cold face, 

 and the plane midway between them, at the times indicated by the 

 abscissas. The horizontal unit is ] T, the vertical unit J — ^ . 



3I\ 



2K 



In Figure 5, the abscissas are values of z, the ordinates are rates of 

 flow. Each curve corresponds to a given epoch, and the epochs repre- 

 sented are | T, ] T, h T, T, 2 T. 



Without waiting to discuss here certain theoretical questions which 

 will present themselves in the course of our work, we may briefly 

 describe some preliminary experiments. 



We have used two different forms of apparatus in our work, the one 

 intended for measuring the absolute thermal conductivities at tempera- 



