1056 Tn A xs ACTIONS of the A:\ierican Institute. 



tlie bottom of the cylinder, by means of a mirror and by two Frcsnel 

 rombs above the cylinder, in such a manner that each will illuminate 

 half of the field with a semi-disk of yellow light more or less intense. 

 These colors are observ^ed with a terrestrial ej^e-piece formed of four 

 glasses, by which the field may be illuminated with perfect uniformity. 

 The colors are proportional to the hight of the columns, if the liquid 

 contains the same proportion of caramel, or in proportion to the 

 richness of the liquid in caramel, if the two columns have the same 

 height. 



Eadiant Heat, 

 Prof. Magnus, in a commnnication to the Berlin Academy of 

 Sciences, gives the results of his experiences on the emission and 

 absorption of heat radiated at low temperatures, Avhich may be thus 

 briefly enumerated : 1. Different substances heated to 150 degrees 

 Centigrade (302 degrees Fahrenheit), radiate different qualities of 

 heat. While there are bodies which radiate only one kind of heat, 

 others radiate many kinds. 2. Pure rock salt (chloride of sodimn) 

 radiates one kind of heat, as the spectrum of sodium shows only 

 one color. It is monothermic, and its vapor monochromatic. 3. It 

 does not permit all kinds of heat to pass through it with equal facility, 

 as stated by Melloni and others ; for it absorbs heat radiated by rock 

 salt more readily than that radiated by silvin (chloride of potassium) 

 and other bodies. The absorbing power increases with the thickness 

 of the rock salt plate. 4. The great diathermancy of rock salt does 

 not depend on a small absorbing power for different kinds of heat, 

 but upon the foct that it radiates only a single kind of heat, and con- 

 sequently absorbs only this, and that almost all other bodies at a 

 temperature of 150 degrees Centigrade, send out heat entirely differ- 

 ent from that of rock salt. 5. Silvin behaves like rock salt, but is 

 not monothermic in an equal degree, and bears some analogy to the 

 colors of its ignited vapors, and the spectrum of potassium, which is 

 almost continuous. 6. Fluor spar almost completely absorbs rock 

 salt heat, yet of its radiant heat only thirty per cent is absorbed by a 

 rock salt plate twenty millimeters thick. However, fluor spar radi- 

 ates three times as much heat as rock salt. 7. If a spectrum of heat 

 radiated at 150 degrees Centigrade, could be formed, and rock salt 

 were the radiating body, only one band would be seen. Silvin would 

 give a more extended spectrum, yet would occupy'- only a simill por- 

 tion of the spectrum radiated from lampblack. 



