202 BIOGRAPHIES OF SCIENTIFIC MEN 



investigation might be made, showing how much heat 

 was given out per hour by the black cloth to the surrounding 

 glass and water. Here thermal energy was communicated 

 to the black cloth by waves of sunlight, and given out as 

 thermometric heat to the glass and water around it. Thus, 

 through the water, there was actually energy travelling 

 inwards, in virtue of waves of light, and outwards through 

 the same space in virtue of thermal conduction. This 

 suggestion respecting radium might be regarded as utterly 

 unacceptable, but, at all events, Lord Kelvin thought it 

 would be conceded that experiments should be made 

 comparing the thermal emission from radium wholly 

 surrounded with thick lead with that found with the 

 surroundings hitherto used. . . . Such were Lord 

 Kelvin's ideas concerning radium. 



