Intelligence and Miscellaneous Articles. 405 



The author regards the absolute limiting value of the magnetic 

 momentum of the unit of length as a physical constant characteristic 

 of iron, and comparable with the constants of elasticity, solidity, 

 &c; and he holds that its existence is quite in accord with the 

 theory of rotatory molecular magnets, of the probability of which he 

 thinks a striking proof has been afforded by his discovery of abnormal 

 magnetization and the phenomena connected therewith. 



The author finally points out that the result of his calculation, 

 contained in the above law, also justifies the conclusion that the pro- 

 portionality indicated by Midler between the coefficient B of his 

 formula and the length of the bar, but considered inaccurate and 

 imperfectly established, must have general validity. At the same 

 time the circumstances are mentioned to which it must be ascribed 

 that both Miiller and the author were led to doubt, from existing 

 data, the applicability and universality of this formula. 



The author refers to a research by Oberbeck which has recently 

 appeared, of which he only heard after his investigation was finished : 

 in it the question of the existence of an independent limiting value of 

 the magnetic momentum of the unit of volume is discussed. But the 

 author remarks that this research involves no change or completion 

 of the results above adduced ; for the amount of the limiting value is 

 neither ascertained nor adduced, and the results of the experiments 

 show too irregular a course to permit a numerical deduction of such 

 a limiting value, although the existence of such a one seems to follow 

 from two of the series of them. — Sitzungsberichte der Kaiserlichen 

 Akademie in Wien, 1869, No .12. 



ON THE REFLECTION OF HEAT FROM THE SURFACE OF FLUOR- 

 SPAR AND OTHER BODIES. BY G. MAGNUS. 



After succeeding in freeing the heat from various substances 

 raised to 150° C. from the rays of the heating-flame and of other 

 heating-bodies, it was possible to show, in the research laid 

 before the Academy on June 9, that there are some bodies which 

 only radiate one or at most a few wave-lengths, others which emit a 

 greater number. Hence it seemed interesting to answer the question, 

 what is the reflecting-power of these bodies ? whether the same dif- 

 ferences which are observed in reference to the absorption and trans- 

 mission of heat by bodies that are identical as regards the action of 

 light also occur in the reflection of heat. 



Differences in reflecting-power can only definitely occur when 

 rays are reflected which only contain one or a few wave-lengths. 

 Such rays have been already obtained by using individual parts of 

 a spectrum produced by a rock-salt prism, or by allowing the rays 

 of a source of heat which radiates many wave-lengths (those of a 

 lamp for instance) to pass through substances which only absorb a 

 certain number. But there are very few substances which transmit 

 rays of only one or of a few wave-lengths ; and these are, moreover, 

 of small intensity. 



