128 THE MICROSCOPE. 



rapid advancement of scientific knowledge, for each 

 new inference may form the starting-point of a fresh 

 line of investigation ; but, on the other hand, every 

 false statement, regarded as an observed fact, forms 

 a terrible barrier to onward progress, since, before 

 the slightest useful advance can be made, it is neces- 

 sary to retrace our steps, it may be for a long way, 

 before we can hope to recommence our onward course. 

 Again, a much greater amount of evidence is always 

 required to overthrow a false conclusion than is 

 sufficient to propagate the original mistake, and 

 there can be no task more unsatisfactory than that 

 of being called upon to controvert the opinions and 

 deductions. of others. Years must be passed in patient 

 investigation before a man can expect to be able to 

 trust himself as an observer of facts, and it is only by 

 careful and unremitting exercise that he will gradually 

 acquire habits of attentive observation and the power 

 of thoughtful discrimination, which can alone render 

 his conclusions reliable. Indeed, though he labour 

 hard and earnestly, he will scarcely have properly 

 educated himself ere his powers begin to decay, and 

 he become liable to err from the natural deterioration 

 in structure of the organs upon which the observation 

 of his facts entirely depends." 



* "How to Work with the Microscope," Fourth Edition, pp. 

 i33, 189. 



