206 ANNUAL OF SCIENTIFIC DISCOVERT. 



tion, and becomes a consequence of it. For if, at a given temperature, a 

 liquid ceases to wet the glass, beyond this temperature the liquid takes a 

 convex surface and depresses itself; whence it follows, that liquids like 

 mercury not wetting the glass at the ordinary temperature, can wet it at a 

 temperature quite low, and so present under the action of cold the same 

 series of phenomena which either presents under that of heat. 



OX THE HEAT-CONDUCTING TOWER OF MERCURY. 



At the recent meeting of the German Association for the promotion of sci- 

 ence, Prof. Frankenheim read a paper " On the Heat-conducting Power of 

 Mercury." The investigations of Fourier and Poisson determined the relation 

 between the phenomena of conduction and those of radiation, the last made 

 uniform by the use of varnishes. Mercury was enclosed in iron tubes, and 

 thermometers, wrapped in thin membranes, plunged into them, the mobility 

 of the mercury having been previously diminished by its amalgamation with 

 small quantities of zinc. A constant temperature could be maintained only 

 after a few hours' waiting. Prof. Frankenheim found that mercury ranked 

 high among the beet metallic conductors, both of heat and electricity. The 

 theoretical views, founded on the lately prevailing supposition that liquid 

 substances possess very little, if any, conductive power, rest on an erroneous 

 argument, attaching excessive importance to the state of aggregation. Ac- 

 cording to Prof. Frankenheim's definition, elasticity in solid and in liquid 

 bodies has this difference : that in the latter the particles may undergo rota- 

 tion without giving rise to the manifestation of any force, while in the former, 

 rotation and manifestation of force are essentially connected. 



ON THE INFLUENCE OF METALS ON RADIANT HEAT. 



The results of a recent investigation on this subject, by Prof. H. Knob- 

 lunch, of Halle, may be stated to be as follows : 



1. Metals, as gold, silver, and platinum, when in thin layers, are to, be 

 regarded as diathermanous bodies, which permit a portion of the calorific 

 rays to pass through them ; which portion naturally becomes less as the 

 thickness of the layer increases. 



tt 



In thus transmitting the calorific rays, certain metals, as gold and silver, 

 exercise an elective absorption, similar to that of colored transparent bodies 

 upon light. Others, on the contrary, like platinum, act in the same manner 

 upon all rays, and are therefore to be regarded as analogous to colorless 

 bodies in the case of light. 



o 



2. In the case of diffuse reflection, also, certain metals, such as gold, 

 silver, mercury, copper and brass, similar to colored and opaque bodies as 

 regards light, exercise an elective absorption upon the calorific rays, in con- 

 sequence of which the properties of the latter are altered. Others, on the 

 contrary, for example, platinum, iron, tin, zinc, lead, alloy of lead, and tin, 

 German silver, reflect all kinds of calorific rays in the same proportion, ex- 

 actly as colorless opaque bodies do with regard to light. 



The properties which distinguish calorific rays reflected from metals, from 

 unreflected heat, are so far dependent on the source of heat, that differences. 



