450 Intelligence and Miscellaneous Articles. 



that of hard. And as heating to temperatures like that of boiling 

 water produces an appreciable annealing, the conducting power 

 of the hard steel determined at a lower temperature would have 

 been even less. 



The electrical conductivity of the two bars was further determined 

 by transmitting a constant current, a branch of which was sent 

 by means of two knife-edges through a sensitive galvanometer in a 

 current of 5000 to 10,000 ohms resistance. The factor of reduction 

 to absolute measure was determined by means of a Clark's element. 

 The conductivities referred to mercury are, according to a measure- 

 ment of Mr. Sheldon, 



k hard = 3*3, soft = 5-5. 



A heated and slowly cooled bar oF wrought iron of the same dimen- 

 sions was investigated. Its conducting power was about 40 per 

 cent, higher than that of soft steel : 



k soft wrought iron = 7*6. 

 That its conducting power was greater in a similar ratio is shown 

 by an experiment in the freezing mixture (see p. 448, note). The 

 height of deposit in hard steel amounted to 72 mm., and in soft 

 steel to 92 mm., and in soft iron to 110 millim. 



We have thus found for the ratio of the thermal conductivity k 

 to the electrical conductivity k : — 



Hard Steel. Soft Steel. 



* = 2^_ 2 =0-019; °JB± = ow. 

 k 3-3 55 



The corresponding numbers with Kirchhoff and Hansemann are 

 for 15° :— 



Bar No. I. No. II. No. III. 



I = °^ 4 1 8 = 0-0208 ; ^° 9G4 = 0-0237 ; ^75 = Q . 

 k 6-803 4-006 6-569 



As my determinations of the thermal conductivity can only lay 



claim to an approximate measurement, the agreement of - cannot 

 be expected to be closer. 



While thus the conductivity of different and differently heated 

 iron and steel may be different, the ratio of the conductivity for 

 heat and for electricity seems to remain about the same. — Wiede- 

 mann's Annalen, No 4, 1888. 



MOUNTAIN FORMATION. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



In your issue of March (p. 210) Mr. T. Mellard Reade publishes 



a very suggestive paper on the " Geological Consequences of the 



Discovery of a Level-of-no-Strain in a Cooling Globe," in which he 



maintains the untenableness of the contractional theory of moun- 



