THE SCIENCE OF MICROSCOPY. 327 



monly excused by attributing it to the use of bad instruments and 

 the general liability to deception of the senses, rather than to 

 special sources affecting the individaal. But it is abundantly 

 manifest that the microscopist is himself more often on the wrong 

 track than his instrument, whether through defective visual power, 

 deficient perceptive power, preoccupation of mind by states of 

 expectancy, or prejudices arising from theoretical hobbies, and 

 let us add, ignorance of theory. But the remedy for this state of 

 things will not be found in the performance of a good instrument 

 unless that performance be better understood. And the advice 

 to abstain from noting or describing what is not clearly seen is at 

 best but of temporary and negative value. If followed it might 

 perhaps save some of the false issues with which science is 

 burdened, though it yet remains to be shown whether such 

 negative gain is not over-balanced by the discouragement thus 

 thrown upon the study of obscure and difficult indications in the 

 microscope image. Like other excellent advice (for instance, 

 Fundi to persons about to marry !) it is inoperative partly because 

 few persons are so distrustful of their sight or judgment as to 

 think the advice necessary in their case, and partly because the 

 remedy would be worse than the fault. For in the first place the 

 phrase *' clearly seen" implies that error of observation lies wholly 

 in not having a clear image before the eye, and thus begs a wide 

 question of principle. Optical illusions are as clearly seen as 

 material objects, and the microscope image though perfectly seen 

 may be an illusion in so far as any inference of material structure is 

 founded upon it. The most perfect optical illusion may be 

 produced with lined or dotted objects whose image is not 

 conformable with the original number, or direction of lines or 

 dots. Yet what is seen is neither confused nor obscure, though 

 details may be added to, or omitted from that which ought to have 

 been seen. And this applies, not only when a bad instrument is 

 used, or incompetent observers describe what they see, but when the 

 most experienced microscopist is looking at any new or unknown 



