TRE ine > an nein ~~ 
ai hel cla aaa 
Thermal Oonductivities of Marble and Slate. 437 
each heating. The steam, after passing through a hot chamber 
A, was led to the outer air by a jacketed pipe, 2, descendino* 
from the bottom of A. i 
The planed upper surface of the chamber is about 70™ square 
and inside the bolt holes of its flanges there is a clear space of 
65™ square. Directly upon this face was laid the first slab of 
marble about 60™ square and 1™ thick. The leads from two 
thermal junctions of platinoid-copper were then stretched across 
the middle of the slab so that the junctions were on the trans- 
verse middle line of the slab, about 1™ from the vertical axis. 
The second slab placed upon these held them firmly in place, 
bearing on the slightly thickened junctions; upon the second 
slab were placed two more thermopiles, and the pile of slabs 
thus built up, to the number of seven, formed a prism about 
60™ square and 7™ thick. Upon the upper slab was placed 
the planed lower surface of the square iron box D, which held 
the ice and water to cool the upper surface, The flanges of 
the upper and lower castings were then bolted firmly together 
and the slabs pressed as closely into contact as possible, the 
average thickness of the slabs being 1° and of the spaces 0°3™, 
i 
D h 
sae G 
; ugh 
L S ame 
Ke [i = 
i 4 ig 5 
Bj: / 
OF Come PTE ecceczas,\ \ om ETL 1 Yet 
eal asl 
FTA [FTX ——. paieaioeices)| ie 
A portion of the upper pan was isolated by soldering a brass 
eylinder 12°3°" in inside diameter with its axis vertical in the 
centre of the pan. This served as a center for a horizontal six- 
armed stirrer actuated by the motor M and provided with stiff 
brushes, which swept over the bottom of the pan twice a min- 
ute, and which carried about 15 kilograms of ice in a wire bas- 
ket reaching within 5™™ of the bottom. The cylinder, which 
was provided with its own stirrer inside and had an elaborate 
system of guards and jackets, which we do not need to describe 
here, served to isolate the heat coming out from a considerable 
surface at practically a uniform temperature near the axis of 
the prism. The amount of ice melted in the cylinder in a given 
* In the diagram, / is represented as ascending and as inserted in the side of A 
