128 GREAT MEN OF SCIENCE 



does not only require a certain temperature, but also a certain 

 quantity of heat, which is always consumed, though it cannot 

 be detected by the thermometer. He proved for example, 

 that when ice becomes water, the thermometer does not rise 

 above zero, although heat is continually added until all the 

 ice is melted; for this reason, also, the ice point is an assured 

 fixed point for the thermometer. Black also measured the 

 'heat of fusion' of ice, and the 'heat of evaporation' of water 

 (he called them the 'latent' heats), and his results are as near 

 to the figures known to us to-day as could possibly be ex- 

 pected from the first practice of a new idea and method of 

 measurement. 'It is scarcely possible to gain a deeper 

 insight by attention to experiences by no means striking and 

 accessible to everyone, than Black does here. Besides a 

 receptive eye for the processes of our everyday surroundings, 

 we have the acute analysis of each single experiment, and skill 

 in the successful application of simple means. '^ 



Black began investigations in calorimetry previously to 

 1760.2 In 1762 he communicated the results to a learned 

 society in Glasgow, and thenceforward described them 

 regularly in his university lectures, whence the ideas spread. 

 A printed publication followed after his death, from his 

 manuscript lectures (1803). 



Black's earliest work related to another matter, in which 



^ E. Mach, Die Prinzipien der Wdrmelehre, Leipzig, 1896, p. 163. 



2 Proof exists that in the year 1760 Black communicated his results to 

 his contemporaries by word of mouth, for example, to Watt as regards 

 the heat of evaporation of water, and its considerable magnitude. From 

 the year 1772 onwards Wilke of Mecklenburg - who also rendered ser- 

 vices to the investigation of electricity - published in the Swedish Aca- 

 demy, experiments relating likewise to consumption of heat in change of 

 state, and in change of temperature of various bodies. He was the first 

 after Black who pointed out the essential features of these questions. 

 Lavoisier and Laplace only came forward with calorimetric work in 

 1780. Very noteworthy in this connection - and otherwise also - is 

 the enthusiastic admiration shown by Lavoisier for Black in his letters, 

 as compared with his avoidance of public mention of Black's name. 

 (See the report of the Editor of Black's Lectures, vol. 3, pp. 21, 31.) 

 Wilke is also only given the date 1781 by Lavoisier. 



