THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. XLI. — The Internal Temperature Gradient of Metals ; 

 by Schuylek B. Sekviss. 



In the Physical Review for October, 1906, Dr. C. B. Thwing 



reported experiments in which he found that cylindrical speci- 

 mens of common materials showed at points 3 cm from their 

 surfaces an excess of temperature above their surroundings, 

 ranging from 0°-000015 in the case of marble to 0°-000308 for 

 aluminum oxide. This he ascribed to their radio-activity. 

 Sow the work of Strutt, Eve, McLennan and Burton, Cooke, 

 Wood, and Campbell, shows that common materials have the 

 power of ionizing air to a slight extent. But Strutt and 

 Rutherford are of the opinion that the feeble radio-activity of 

 common materials is a superficial rather than a volume effect, 

 so further experiments seemed advisable. Thus far the results 

 have been entirely negative. 



In the meantime H, Greinacher has reopened the subject by 

 publishing in the Annalen der Physik for October, 1907, an 

 interesting computation of the magnitude of the effect to be 

 expected, showing that Dr. Thwing's results are much too 

 large. It has, therefore, seemed worth while to publish these 

 experimental results immediately, without waiting for the com- 

 pletion of certain other experiments of rather a different sort, 

 which were to have been made. 



Since the value of any work of this sort is entirely dependent 

 upon the accuracy of the manipulation, the reader must pardon 

 even a tedious fullness of detail in the description of apparatus 

 which follows : 



Am. Jour. Sci. — Fourth Series, Vol. XXIV, No. 144. — December, 1907. 

 32 



