COUNT EUMFORD. 157 



up by different substances in humid air. Sheep's wool 

 he found to be the most absorbent, while cotton wool 

 and ravellings of fine linen were among the least. These 

 experiments he regarded as of the highest importance, 

 as they explained, to his mind, the salubrity of flannel 

 when worn next the skin. Its healthfulness he ascribed 

 to its power of taking up the moisture of the body, 

 sensible and insensible, and dispersing it by evaporation 

 in the air. 



The propagation of heat in fluids was but imperfectly 

 understood when Eumford took the subject up. In 

 various parts of his writings he dwells on the importance 

 of what he calls accidental observations, deeming them 

 more fruitful than those which have sprung from the 

 more recondite thoughts of the philosopher. But acci- 

 dents, however numerous, if they fail to reach the 

 proper soil are barren. Eumford ascribed to accident 

 the investigations now referred to. He had been experi- 

 menting upon liquids, employing bulbs of copper with 

 glass tubes attached to them. On one occasion, having 

 rilled his bulb and tube with spirits of wine, and heated 

 the liquid, he placed it to cool in a window where the 

 sun happened to shine upon it. Particles of dust had 

 found their way into the spirit, and the sun, shining on 

 these particles, made their motions vividly apparent. 

 Along the axis of his tube the illuminated particles rose ; 

 along its sides they fell, thus making manifest the 

 currents within the liquid. The reason of this circula- 

 tion is obvious enough. The glass tube in contact with 

 the cold air had its temperature lowered. The glass 

 drew heat from the liquid in contact with it, which 

 thereby being rendered more dense, fell along the sides 

 of the tube, while, to supply its place, the lighter liquid 

 rose along the axis. The motion here described is 



