AIM AND PROGRESS OF PHYSICAL SCIENCE. 345 



individually acquired, a result of experience, of training, the 

 recollection of former acts of a similar kind. 



This completes the circle of our observations, and lands us 

 at the spot whence we set out. We found at the beginning 

 that what physical science strives after is the knowledge of laws, 

 in other words, the knowledge how at different times under the 

 same conditions the same results are brought about ; and we 

 found in the last instance how all laws can be reduced to laws of 

 motion. We now find, in conclusion, that our sensations are 

 merely signs of changes taking place in the external world, and 

 can only be regarded as pictures in that they represent succes- 

 sion in time. For this very reason they are in a position to 

 show directly the conformity to law, in regard to succession 

 in time, of natural phenomena. If, under the same natural 

 circumstances, the same action take place, a person observing it 

 under the same conditions will find the same series of impressions 

 regularly recur. That which our organs of sense perform is 

 clearly sufficient to meet the demands of science as well as the 

 practical ends of the man of business who must rely for support 

 on the knowledge of natural laws, acquired, partly in voluntarily 

 by daily experience, and partly purposely by the study of 

 science. 



Having now completed our survey, we may, perhaps, strike 

 a not unsatisfactory balance. Physical science has made active 

 progress, not only in this or that direction, but as a vast whole, 

 and what has been accomplished may warrant the attainment of 

 further progress. Doubts respecting the entire conformity to 

 law of nature are more and more dispelled ; laws more general 

 and more comprehensive have revealed themselves. That the 

 direction which scientific study has taken is a healthy one its 

 great practical issues have clearly demonstrated ; and I may here 

 be permitted to direct particular attention to the branch of science 

 more especially my own. In physiology particularly scientific 

 work had been crippled by doubts respecting the necassary con- 

 formity to law, which means, as we have shown, the intelligi- 

 bility of vital phenomena, and this naturally extended itself to 

 the practical science directly dependent on physiology, namely, 



