232 Mr Fox on the Steam Condensed in different Vessels. 



loss of the visible object answers to £T/7oX?j. I do not mean 

 to assert that these terms are never misapplied ; but Strabo 

 has not been guilty of this critical inaccuracy ; their very exist- 

 ence proves the reality of the separate ideas ; and this is in 

 itself sufficient to show that there is no foundation for what 

 Dr Horsley has mistaken for a discovery of great use to the 

 chronologist. 



S. P. R. 

 Oxford, July 1828. 



Art. VI. — On the relative quantities of steam condensed in 

 vessels with bright metallic and blackened surfaces. By 

 R. W. Fox, Esq. Vice-President of the Royal Geological 

 Society of Cornwall. Communicated by William J. Hen- 

 wood, F. G. S. 



Two cubical vessels of tin plate, of which the surface of one 

 was bright, and that of the other covered with lamp-black, 

 were connected with a steam boiler, by tubes so inclined to- 

 wards the latter as to allow all water obtaining from conden- 

 sation in the tubes to return to it. The vessels were of equal 

 dimensions, four inches side, and the experiment was made 

 in a close room, of which the temperature was 52° ; that of the 

 steam being at a mean of 215°. The water was withdrawn by 

 cocks properly adjusted for the purpose ; and at the expiration 

 of seventy-two minutes, the bright vessel had afforded 5.7, and 

 the blackened one 10.2 cubic inches. Now, supposing steam 

 of this temperature to be 1600 times rarer than water, in twenty- 

 four hours the condensation from one foot of blackened surface 

 would be 489600 cubic inches, or 1736 gallons of steam, and 

 from an equal extent of bright metallic surface 273600 cubic 

 inches, or 972 gallons. Hence the condensing energies of a 

 blackened and polished metallic surface were to one another 

 as 1736 is to 972. When the difference between the tempera- 

 ture of the heated body and that of the surrounding medium 

 is greater, the effect will be proportionally augmented. 



But when currents obtain it is probable that the effect will 

 be increased in both ; but that the ratio of this increase will 



