210 PROCEEDINGS OF THE AMERICAN ACADEMY 



Ihvestigaiions on Light and Heat, puBtisHfa) with Appropriation fbom thb 



KUMFOBD Fund. 



XllL 



CONTRIBUTIONS FROM THE PHYSICAL LABORATORY OF 

 HARVARD UNIVERSITY. 



INFLUENCE OF MAGNETISM UPON THERMAL CON- 

 DUCTIVITY. 



By John Trowbuidge and Charles Bingham Penrose. 



Presented May 29th, 1883. 



The following experiments were made in order to test Maggi's 

 results * in regard to the effect of magnetism upon the thermal con- 

 ductivity of iron. Maggi's conclusions have never been confirmed, and 

 have been much doubted by other observers. The experiments of 

 Sir W. Thomson, t in which he found that longitudinal magnetization 

 diminished, while transverse magnetization increased the electrical 

 conductivity of iron, afford — from the fact that electrical and thermal 

 conductivities are in general proportional — the chief confirmation of 

 Maggi's results. The experiments of Thomson have, however, been 

 questioned. 



In the method employed by Maggi, a circular plate of soft iron 

 was placed horizontally upon the poles of a vertical horseshoe magnet. 

 Through the centre of the plate passed a lead tube conveying steam. 

 The surface of the plate was covered with a mixture of oil and wax. 

 When the magnet was made, the melted wax was bounded by an 

 ellipse. If the conductivity had been equal in all directions, it would 

 have been bounded by a circle. The long axis of the ellipse was 

 perpendicular to the line joining the two poles ; the short axis was 

 parallel to the line. The ratio of the axes was G : 5. The two 

 poles were separated from the iron plate by paper. In order to 

 compensate for the direct effect of the poles upon the flow of heat, 

 two bars of soft iron were placed symmetrically beneath the plate, at 

 the extremities of the diameter, perpendicular to the line j nning the 

 poles. No effort seems to have been made to avoid the effect due 



* Bibl. Univ. Archiv., 1850. t Pliil. Trans., vol. cxlvi. 



