14 PROGRESS OF HUMAN KNOWLEDGE. 



While recognising these results of the human intellect 

 as best marking man's place in creation, it is needful to 

 note how few there are capable of reaching them. In 

 comparison with men thus endowed, able to bring their 

 endowments into action, how endless the multitudes of 

 all times and races of men, the cyphers of creation, 

 who tenant the earth in successive generations, without 

 leaving traces of their existence behind ! 



A clearer perception of the instantice crucis, grow- 

 ing out of the more rigid demand for proofs, is one of 

 the characteristics of modern science. The value of 

 these cannot easily be overrated. Kept closely before 

 the mind, they give stability to actual knowledge, and 

 starting-points for its future extension. There is no 

 single well-assured truth, however limited its seeming 

 import, which may not become the germ of others. It 

 is a part of wisdom to store the mind with instances of 

 this kind, which appertain to general philosophy and 

 theology as well as to physical science. The simpler 

 such instances are the better. If encumbered with 

 details, their pertinency and practical value are pro- 

 portionally impaired. 



In a record of the progress of the physical sciences 

 it is fitting to note the curious halts or arrests often 

 occurring in connexion with some particular theory or 

 fresh discovery of facts. Many retrospective instances 

 might be given of these unstable resting-places in our 

 knowledge. The doctrine of Phlogiston in its origin 

 and fate is one of the most familiar. The doctrines 

 of Elective Affinity held by the earlier chemists, and 



