568 



ideal method foi- producing cliilled metal. If any object has been 

 covered in this way with "zinc", tliis layer is in a inetastable con- 

 dition aftei' cooling to ordinary temperature. 



In consequence such a layer will disintegrate in the long run. 

 That the metal made in this way is not in the ordinary condition 

 is proved by experience. Nf.l burger ^) says about it (in the case 

 of tin) : 



••.... ebenso erleiden diese uriter Umstanden auch eine teilweise 

 Veranderung ihrer physikalisclien Eigenschaften, die in einer Ver- 



grösserung der Harte besteht Wahrend gegossenes Zinn nach 



der BRI^ELLSCHEN Kugeldruckprobe einen Hartegrad von 9.5 aufweist, 

 zeigt gespritztes einen solchen von 14.2". 



We hope to be able to report shortly on the metastability of 

 these "atomized" metals. 



VAN 't Hoff — Laboratory. 



Utrecht November 1913. 



Physics. — "A rapid Thermopile" By Dr. W. J. H. Moll. (Com- 

 municated by Prof. W. H. Julius.) 



Among the many instruments, which have been devised for the 

 quantitative investigation of visible and invisible radiation, the thermo- 

 pile occupies the foremost place in order of both priority and 

 merit. Though for special researches and under particular circum- 

 stances the bolometer and the radiometer may be deemed more 

 suitable, the thermopile has never ceased to find its application, for 

 the most delicate measurement as well as for the simple demon- 

 strative experiment. 



It is particularly of late years, that it has once again attracted the 

 attention of a number of investigators, and that numerous improve- 

 ments in its construction have been tried. All of these had the same 

 purpose, namely to increase the sensitiveness of the instrument. 



Another property, however, is by no means of less importance, 

 viz. the rapidity with which, after the radiation has been admitted 

 or intercepted, thermal equilibrium is reached in the pile. The greater 

 this rajjidity, the better is the instrument adapted to the invest- 

 io-ation of all sorts of radiation-phenomena of short duration and of 

 rapid variability, and also to those researches which require a long 

 series of successive readings, and which with a slow instrument 



1) Die Naturwissenschaften, I, 465 (1913). 



