130 MEMOIR OF DR. DALTON, AND 



We find Sennertus, about the same time, expounding 

 Aristotle's opinions on the elements, and looking to the 

 authority of character more than experiment, but he does not 

 give a fifth element such as Aristotle's ether. The argument 

 he gives that there are only four is curious, and another of the 

 interminable varieties of method in which vagueness thinks. 

 " There are two right motions, one from the mean, the other 

 to the mean, there will, therefore, be an equal quantity of 

 simple bodies, subject to these two simple motions, one which 

 absolutely is heavy, called earth ; another absolutely is light, 

 called fire. But because nature wishes the world to be one, 

 but contrary extremes cannot constitute one, she always 

 couples the extremes by means (per media), and connects the 

 last of the superior kind with the first of an inferior. This 

 mean is therefore required. But this cannot be one. Because, 

 if so, it would occupy the mean place between the extremes, 

 or between the centre and circumference, and so no right 

 motion (rectus motus) could be given to it. For it could 

 neither be moved to the middle, nor from the middle, nor 

 could it be called more or less heavy. It is necessary, there- 

 fore, to have two means, one light, and which may be moved 

 from the middle upward, in respect of which it is heavy, and 

 is called air ; the other heavy, and tending to the middle, in 

 respect of which it is light, which is called water. There are, 

 therefore, four elements, fire, air, water, earth. There cannot 

 be a fifth for the same cause, that there cannot be only one 

 mean. But if any one will desire to establish five, his senses 

 and experience disprove it." * 



He endeavours to establish a difference between the pure fire 

 and the common drudge of life, and quotes Scaliger to support 

 him, but in neither of them do we find any distinct ideas of 

 what these difi'erences consist. We are confounded by the great 

 part which hot, cold, moist, and dry, have to play, and it 



* Danielis Sennerti Vratislavien&is Epitome Naturalis Scieniiae, Oxoniae, 

 J 632. Page 185. 



