1883.] on Count Rumford, Originator of the Royal Institution. 445 



other matters upon light, or rather the action of light on the green 

 leaves of plants. From this inquiry he turned to estiuiate the t|uantities 

 of moisture taken up by ditferent substances in humid air. Sheeps' 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 Rumford took the subject up. In various parts of his writings, 

 lie 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 accidents, however 

 numerous, if they fail to reach the proper soil are barren. Rumford 

 ascribed to accident the investigations now referred to. He had been 

 experimenting upon liquids, employing bulbs of copper with glass 

 tubes attached to them. On one occasion, having filled his bulb and 

 tube with S23irits 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 sj^irit, 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 circulation 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 placo, the lighter 

 liquid rose along the axis. The motion here described is exactly that 

 of the great geyser of Iceland. The water falls along the sides of the 

 geyser tube, and rises along the axis. In this way then heat is pro- 

 pagated through liquids. It is a case of bodily transport by currents, 

 and not one of true conduction from molecule to molecule. 



It immediately occurred to Rumford to hamper this motion of 

 convection. He called to mind an observation he had made at Baise, 

 when the water of the sea being cool to the touch, the sand a few 

 inches below the water was intolerably hot. This he ascribed to the 

 impediment offered by the sand to the upward diffusion of the heat. 

 The length of time required by stewed apples to cool, also occurred 

 to him. He had frequently burnt his mouth by a spoonful of apple 

 taken from the centre of a dish after the surface had become cool. 

 He devised thermometers with a view of bringing his notions to an 

 experimental test. With pure water he compared water slightly 

 thickened with starch, water containing eider-down, and stewed apples 

 bruised into a pulp which consisted almost wholly of water. In all 

 cases he found the propagation of heat impeded, and cooling retarded, 

 by everything that prevented the formation of currents. As he pur- 

 sued his inquiries, the idea became more and more fixed in his mind 

 that convection is the only means by which heat is diffused in liquids. 



