26 HOW TO WORK 



structure after having been submitted to these four modes of examina- 

 tion, should be contrasted with the idea which would have been 

 formed of it if an observation had been made by one mode of illu- 

 mination only. But before this can be practically carried out, it is 

 necessary to describe how objects are to be examined in various 

 media. The student must therefore refer to 136 to 143. 



OF DRAWING AND ENGRAVING OBJECTS. 



41. Of Drawing objects. It may be truly said that no real 

 advance in our knowledge of the minute structure of animal or 

 vegetable tissues, can be communicated to others, unless accurate 

 drawings are made, for it is almost hopeless for an observer to attempt 

 to describe what he sees in words, and such descriptions, however 

 careful they may be, scarcely admit of comparison with those of 

 other persons. On the other hand, a truthful drawing of what a man 

 has seen recently, may be compared with drawings which may be 

 made a hundred years hence, and although the means of obser- 

 vation will be far more perfect than they are at present, such 

 comparisons may be useful in many ways, and especially in 

 preventing erroneous conclusions. By description alone ingenious 

 persons who take the pains may so express themselves as to render 

 it very doubtful what their opinion really is, but if they can only be 

 persuaded to make a drawing, there can be no doubt concerning 

 the exact nature of their view. I think that an honest enquirer 

 cannot be of greater use in his time than by making good drawings 

 of what he has seen, and we may feel sure that those who follow us 

 will respect our drawings, if honest copies of nature, although very 

 little of what is now written will be read some years hence, when the 

 whole aspect of our department of science shall be changed. 



In delineating an object magnified by the microscope it is 

 important to copy it correctly, both as regards the relative position of 

 the several parts to one another, and also with respect to size. 

 To copy the size exactly will be found extremely difficult by the eye 

 alone, but there are several ways of proceeding by which accuracy 

 may be ensured. Some of these I shall now briefly describe. The 

 simplest method is to place the paper upon the same level as the 

 stage upon which the object is situated. If we now look steadily at 

 the object with one eye, while the other is employed to govern the 

 movements of the pencil, the object appearing to be thrown as it 

 were, upon the paper, its outline may be very readily traced. By a 

 little practice the relative size of objects may be insured in this 

 manner, but it is troublesome and difficult to keep the image of the 

 object perfectly still. 



