70 Dr Stark on the Injluence of Colour on Heat. 



gard to heat. He used for this purpose a mercurial thermometer, 

 the bulb of which was about j%% of an inch in diameter, and its 

 tube about ten inches in length. This was suspended in the 

 axis of a cylindrical glass tube about three quarters of an inch 

 in diameter, ending with a globe of 1 /^ inch in diameter, in 

 such a manner that the centre of the bulb of the thermometer 

 occupied the centre of the globe. The space between the in- 

 ternal surface of the globe and the surface of the bulb of the 

 thermometer was filled with the substance whose conducting 

 power was to be determined. The instrument was now heated 

 in boiling water, and afterwards, being plunged into a freezing 

 mixture of pounded ice and water, the times of cooling from 70"* 

 to 10° of Reaumur were observed and noted down.* The mat- 

 ters operated upon were raw silk, sheep's wool, cotton wool, 

 linen in the form of the finest lint, fur of the beaver, fur of a 

 white Russian hare, and eider down, sixteen grains in weight of 

 each. The difference in the results from these articles was ex- 

 tremely small, and much less than the Count expected to find 

 them, probably from all the articles being nearly of the same 

 colour, and though of the same weight of different bulk, or oc- 

 cupying a larger space. Of the seven substances, liare'^sfur and 

 eider down were the warmest ; after these came beaver'^s Jitr, 

 raw silk, sheep's wool, cotton wool, and lastly lint or the scrap- 

 ings of fine hnen.-f- 



Hare's fur, . . . 1315" Sheep's wool . . . 1118" 



Eiderdown, . . . 1305" Cotton, 1046" 



Beaver's fur, . . 1296" Linen, 1032" 



Raw silk, .... 1284" 



In the year 1804, Count Rumford communicated to the 

 Royal Society another interesting series of experiments on the 

 nature of heat and the mode of its communication. These 

 experiments were made with hollow brass cylinders filled with 

 water, and coloured with various substances. A thermometer 

 was attached to the cylinder, and the rate of cooling marked. 

 Numerous experiments with the various substances used are de- 

 tailed ; but the most striking one, in the Count's opinion, was 

 that in which the cylinder was blackened, by holding it over 



• Rumford's Essays, vol. ii. p. 430. Lond. 1798. 

 -f- Ibid. p. 437. 



