THE AIM AND ACHIEVEMENTS OF SCIENTIFIC METHOD. 95 



It is well known that physicists have repeatedly attempted 

 a reduction of the happenings of the physical universe in terms 

 of the concepts of mass and motion. This chapter will be 

 devoted to a brief analysis of the main features of these 

 attempts. 



39. 



We have seen that "the investigators of the seventeenth 

 and eighteenth centuries had reached clear concepts of the 

 temperature of a body as its real state of hotness or coldness, 

 and of heat as an hypothetical substance whose transference 

 from one body to another renders intelligible the changes of 

 temperature that ocfcur when bodies are brought near to one 

 another. Black, to whom this concept in its. modern form is 

 due, has the credit of applying it to phenomena many of 

 which he 'himself discovered which before his consideration 

 had not received adequate theoretical explanation. The most 

 important of these were the phenomena attending the trans- 

 formation of a substance from the solid to the liquid, or from 

 the liquid to the gaseous condition. If (for example)* a pot 

 of water is heated above a steady flame its temperature will 

 not rise indefinitely. When the " boiling point " has been 

 reached the whole of the water will be converted gradually 

 into steam the most interesting fact (unknown before Black's 

 researches) being that the temperature of the steam is no 

 higher than that of the water. The constant and fairly regular 

 rise of temperature before the boiling was attributed to a 

 regular transference of heat from the flame to the water. It 

 would be contradictory to suppose that this transference ceased 

 when the water began to boil, f Consequently, since the heat- 

 substance is not "sensible" in the form of an increased 

 temperature of the water or steam, it must have entered into 

 a special combination with the particles of the water a 



* Black, Treatise on Chemistry, 1803, i, p. 164. 



