401 Intelligence and Miscellaneous Articles. 



and Knoblauch allege, it does not transmit all kinds of heat equally 

 well. 



5. Absorption by rock-salt increases with the thickness of the ab- 

 sorbing plate. 



6'. The great diathermancy of rock-salt does not depend upon a 

 small absorbing-power for different kinds of heat, but upon the cir- 

 cumstance that it only emirs one kind of heat and only absorbs 

 this one, and that almost all other bodies at a temperature of 150° C. 

 emit heat which only contains a small portion, or none at all, of the 

 rays which rock-salt emits. 



7. Sylvine behaves like rock-salt, but is not monothermal to the 

 same extent. In this case also we have an analogy with its ignited 

 vapours or those of potassium, which is known to give an almost con- 

 tinuous spectrum. 



8. Fluor-spar absorbs the pure heat from rock-salt almost com- 

 pletely. It would thence be expected that the heat which it emits is 

 also strongly absorbed by rock-salt ; yet 70 percent, passes through 

 a rock-salt plate 20 millims. thick. Taking into consideration the 

 sum of the heat which fluor-spar emits, which is more than thrice as 

 much as that of rock-salt, this phenomenon might be explained; but 

 it needs further investigation. 



9. If it were possible to construct a spectrum of the heat radiated 

 at lf>0° C, and if rock-salt were the substance, the spectrum would 

 contain only one band. If sylvine were used for radiation the spec- 

 trum would be more extended, but would only occupy a small por- 

 tion of that which would result from the heat radiated by lampblack. 

 — Berliner Monatsberickt, June 1869. 



ON THE LIMITS OF THE MAGNETIZATION OE IRON AND STEEL. 

 BY PROF. A. WALTENHOEEN. 



The author has subjected to exhaustive calculations the whole of 

 the present materials of observation on the connexion between elec- 

 tromagnetism and current- intensity, and has thus arrived at the fol- 

 lowing result. 



The limiting value of the magnetic momentum of the unit of weight 

 corresponding to the condition of magnetic saturation of iron is an 

 absolute constant (that is, independent of the shape and magnitude 

 of the electromagnet) whose numerical value amounts to very nearly 

 2100 absolute units per milligramme. 



It follows from this that the theoretically possible temporary 

 magnetization of iron is more than five times as much as the perma- 

 nent which has been attained by the best steel magnets, if, with M. 

 Weber, we take the latter as 400 absolute units per milligramme. 



The author considers it remarkable that just this degree of satu- 

 ration is also that required by the law which he discovered in ISG'S, 

 in reference to the temporary magnetization of steel bars by means 

 of the electrical current ; while, in the case of iron, Lenz and Jacobi's 

 law of proportionality, as the author shows, only holds up to a degree 

 of saturation of (on the average) 800 absolute units per milligranim 



