PEIRCE ANP VVILLSON. — THERMAL CONDUCTIVITIES. 49 



Experiment (a). A compound slab, made up of slabs Z? and A with 

 their thermal elements, was placed between two other glass plates to form 

 a prism. The thickness of B is 0.950 cm. and of A 0.935 cm. In the 

 final state of the prism, the thermal elements on the warmer face of B, 

 between B and A, and on the colder side of A, indicated 88°. 1, 63°. 4, 

 and 38°. 9 respectively. A fall of 14°. 7 in 0.950 cm. is very nearly equal 

 to a fall of 14°.5 in 0.935 cm. 



Experiment (b). In the final state of a prism made up of slabs A and 

 B shut in between two other glass plates, the thermal elements on the 

 warmer face of A, between A and i?, and on the colder face of B, 

 indicated 85°.0, 62°.2, and 39°. 1 respectively. A fall of 22°. 8 in 

 0.935 cm. is very nearly equal to a fall of 23°. 1 in 0.950 cm. 



Experiment (c) . Three slabs A, C, and E of the standard glass with 

 three other glass plates, which we may denote by F, Q, and H, were 

 built up into a prism PA Q C E R with thermal elements between P and 

 A, A and Q, Q and (7, E and R. In the final state the temperatures 

 of the thermal elements were very nearly 88° .2, 74°. 2, 58°.8 and 30°.0, 

 respectively, so that the gradient in the slab A of thickness 0.935 cm. is 

 almost exactly the same as in the double slab G E oi thickness 1.93 cm. 

 There seemed to be, therefore, no appreciable contact resistance (Ueber- 

 gangswiderstand) between the two slabs. 



Experiment (d). After experiment (c) had been finished, a narrow 

 ring of blotting paper, the inside diameter of which was only slightly less 

 than the diameter of the disks, was inserted between C and E so as to 

 have a dead air space between them 0.7 mm. thick, when the prism was 

 under pressure. In the final state the temperatures were now 89°. 9, 

 78°. 3, 66°. 5, and 25°. 9, so that in this particular case the dead air space 

 was nearly equivalent to a glass plate 4.8 mm. thick. 



Experiment (e). In this experiment Plate III., of 0.875 cm. thick- 

 ness, was a part of a prism heated in the larger apparatus intended for 

 the determination of absolute conductivities. The temperatures of the 

 thermal elements on the faces of the plates in the final state were 69°. 7 

 and 58°.8 respectively. In 9060 seconds 464.5 grams of ice were melted. 

 Assuming the area of the bottom of the ice pot to be 126.7 square centi- 

 meters and the latent heat of melting of ice to be 79.25, this corresponds 

 to a conductivity of 0.00258. It is obvious, however, that the last 

 figure of this number is not quite definitely determined. 



VOL. XXXIV. — 4 



