116 MEMOIR OF DR. DALTON, AND 



On the four elements we have occasionally opinions which 

 may be called definite, as when they are said to form various 

 combinations with various properties, but these are held with 

 no tenacity. In the salt, sulphur, and mercury, we have a 

 clue to definite composition, but we have seen them spiritua- 

 lized and held with still less tenacity. In the elements of 

 Leucippus, Democritus, and Lucretius, we have a definite 

 view taken of the subject, but that was soon neglected, to 

 be revived in part when alchemy was falling. We have had 

 an approach to a distinct view before us in that of forces, or 

 unextended points, forming the origin of matter, brought for- 

 ward later, and, perhaps, in an entirely original form, but at 

 least more detailed, by Boscovich. 



