584 APPENDIX. 



frequently expressed by the same individuals, but in a concealed form. It i 

 supposed that nothing more is requisite for microscopical investigation than a 

 good instrument and an object, and that it is only necessary to keep the eye over 

 the eye-piece, in order to be aufalt. Link expresses this opinion in the preface 

 to his phytotomical plates : " I have generally left altogether the observation to 

 my artist, Herr Schmidt, and the unprejudiced mind of this observer, who is 

 totally unacquainted with any of the theories of botany, guarantees the correct- 

 ness of the drawings." The result of such absurdity is, that Link's phytotomi- 

 cal plates are perfectly useless; and, in spite of his celebrated name, we are 

 compelled to warn every beginner from using them, in order that he may not be 

 confused by false views. Link might just as well have asked a child about the 

 apparent distance of the moon, expecting a correct opinion on account of the 

 child's unprejudiced views. Just as we only gradually learn to see with the 

 naked eye in our infancy, and often experience unavoidable illusions, such as that 

 connected with the size of the rising moon, so we must first gradually learn to 

 see through the medium of the microscope, and the more so as the latter is a 

 much more difficult instrument than our eye, owing to the isolation of the objects, 

 and of the absence of the possibility of comparison, as also on account of the 

 necessity that compels us to exclude the use of one eye. We can only 

 succeed gradually in bringing a clear conception before our mind of that which 

 we have physiologically seen ; and just as it is easier for us to put ourselves right 

 in a foggy day, or in a moon-illumined region, if we have already frequented the 

 spots where they occur under other kinds of illumination, and are accurately 

 acquainted with their separate parts, so it will be only possible for a man to make 

 useful microscopical observations, who has not only made himself perfectly fa- 

 miliar with science in general, but has also paid especial attention to the particular 

 objects which he subjects to his examination. It is in consequence of these pre- 

 judices that microscopical discoveries progress so slowly, and that they are generally 

 only admitted in science long after their announcement. For most observers desire 

 to see at a glance what has been done by others, and do not consider that it fre- 

 quently requires years of most active research before an accurate result can be 

 obtained, and that, even after it has been found, that it may require weeks of study 

 before we are able to follow the course traced out by the hand of a master. 

 Hence have arisen the many silly objections made to that greatest of microsco- 

 pical observers, Ehrenberg. 



The above observations will not only enable us to trace the two injurious pre- 

 judices which impede the proper use of the microscope to their source, but we 

 may also deduce from them the leading principles which should guide us in 

 microscopical researches. 



First of all, we must once more compare the impression of light derived from 

 the microscope, with the act of seeing by our eye. The eye, as already observed, 

 only gives us the perception of a luminous or coloured surface. This impression, 

 however, could scarcely be called by us a sight of the corporeal world, if we (as 

 is the case with simple elementary observations) only saw with one eye. But, 

 firstly, our eye is moveable, and we may wander about with it among the objects. 

 Whilst our rolling eye passes over a number of objects, they produce different 

 impressions on our retina at each successive moment, and each successive im- 

 pression falls upon different parts of the retina. Secondly, we do not see with 

 one eye alone, but with two. There belongs, as it were, a particular mode of 

 viewing things to each eye, but habit combines both the images so received (but 

 which mathematically can never entirely cover one another) into a central one. 

 It is only when both impressions impinge on unaccustomed parts of the retina 

 that they produce different perceptions, in the same manner as we feel a small ball 

 double, if we touch it simultaneously with the external sides of the points of two 

 fingers. We further see with two moving eyes, by which the number of intuitive 

 elements connected with an object are increased. Finally, we are able to move 

 ourselves or the objects, and thus to gain quite different views of one and the 

 same object. Thus we obtain a tolerably broad basis upon which a construction 

 of the figure of objects may be confidently undertaken. Practice in this case 

 makes the master, and we see a great difference between a learned man, who has 

 spent the greatest part of his life in his study, and the sportsman, or still more, 



