NATURAL AND PHYSICAL SCIENCE, 1700-1800 313 



and then emptied of steam, and it was largely by the aid of 

 Black's studies on latent heat that Watt was enabled and en- 

 couraged to persevere and push to completion his own epoch- 

 making discoveries in steam engineering. 



Black was also the first to recognize and investigate what we 

 know today as "specific" heat and, by means of a cavity in a block 

 of ice into which various heated bodies were brought, to weigh the 

 water each would produce while cooling from the same tempera- 

 ture, in other words to invent and use the calorimeter. 



EIGHTEENTH CENTURY RESEARCHES ON LIGHT. These start 

 from the great work of Newton, and especially of Huygens, in 

 the previous century, and continue with the fruitful inventions 

 of the achromatic telescope by Hall in 1733, and the work of 

 Dollond, an English optician, upon achromatic lenses, leading 

 up to the construction in 1758 of achromatic telescope objectives. 

 The achromatic telescope now became a serviceable instrument, 

 but the compound microscope had to wait more than half a cen- 

 tury longer for correspondingly serviceable achromatic objectives. 

 It was not until the opening of the nineteenth century that much 

 further progress was made in our knowledge of light. It is 

 rather for progress in sound, in heat, and in electricity, that 

 eighteenth century physical science is chiefly notable. 



BEGINNINGS OF MODERN IDEAS OF ELECTRICITY AND MAG- 

 NETISM. The seventeenth century had witnessed no great 

 progress in these subjects, and the sixteenth century work of 

 William Gilbert stood as almost the only important contribu- 

 tion to our knowledge of them until about 1730. Von Guericke, 

 following suggestions of Gilbert, had, it is true, made a rude 

 electrical machine which he described in a work published in 

 1672, and had observed the electric spark, which with his machine 

 was so small as to be seen only in the dark and to be heard with 

 difficulty. Much more important were the observations of Francis 

 Hawksbee (or Hauksbee), "one of the most active experimental 

 philosophers of his age," and one of the first to study capillary 

 action, who in 1705 communicated to the Royal Society several 

 curious experiments on what he called " the mercurial phosphorus," 



