10 SPECIAL RESULTS OF OBSERVATION IN THE DOMAIN 



causal connection. Such a tendency to advance continu- 

 ally towards the comprehension of the plan of the Universe, 

 or the order of Nature, commences with the combination 

 and generalisation of particular facts ; with the recognition 

 of the conditions under which phenomena, i. e. the mani- 

 festations of physical alterations, are always reproduced in a 

 similar manner : it conducts to the thoughtful consideration 

 of the materials supplied by observation and experiment ; 

 but it does not conduct to a " view of the Universe derived 

 from speculation and the development of thought alone, or 

 to a science or doctrine of the unity of Nature apart 

 from experience." We are, I here repeat it, still far 

 from the time, when it may be thought possible to concen- 

 trate all the perceptions of our senses into the unity of 

 one comprehensive idea embracing the whole of Nature. 

 The safe path was perceived a full century before "Francis 

 Bacon, by Leonardo da Yinci, and indicated by him in a 

 few words : " Comminciare dalF esperienza, e per mezzo di 

 questa, scoprirne la ragione." ( 8 ) In many groups of phse- 

 nomeria we must, indeed, still content ourselves with a 

 deduction of empirical laws ; but the highest object of all 

 investigation into nature, though seldom attained, is the 

 discovery of physical causes. ( 9 ) This is most satisfac- 

 torily and conclusively accomplished, when it is possible 

 to connect the laws of phenomena with the causes which 

 explain them, by the intervention of mathematical rea- 

 soning. It is, however, only in some particularly fa- 

 voured parts of natural science that the "physical descrip- 

 tion" coincides with the "physical explanation of the 

 universe." The two expressions cannot yet be regarded 

 as identical. The inherent grandeur and solemnity of that 



