PREFACE 7 
such lessons as these is vivid experience, not intellectual feats ; 
hence the pupil is constantly told to “ notice” this or that point, 
that is, to corroborate a fact stated; and the exercises are so 
planned as to keep such balance between facts discovered and 
facts verified that when the work is finished on any one object 
that object will stand out in the pupil’s mind as a distinct and 
complete whole. 
Never review an old lesson before beginning a new one. The 
time thus spent is worse than wasted. The mental image of an 
object as such is not necessary to the mental image of another 
object. It is not the mental images that are carried over from 
lesson, to lesson, but the mental processes by which a thing in the 
thing world is translated into a thought in the thought world ; 
these are left as an increasing residuum after each lesson, and 
are ever ready to seize and assimilate the new. Nothing is 
gained by stirring up a sediment of old memory images as a 
preliminary to the new work, and time, interest, and freshness 
are lost. 
But when the whole set of lessons is complete, we have in 
hand material for a general survey or summary of all that has 
been done, and a summary far more rich and interesting because 
summarizing is quite a new kind of thing for the child to do. 
Each plate tells a story, and each stands as an example of 
simple and straightforward description. Lach line in a scientific 
drawing should be a language correlative in the description of 
the object studied. If the pupil describes a leaf as having a 
midrib, veins, serrate edge, his pencil should say these things 
with the same clean-cut accuracy. The plates stand as models 
of arrangement and description, and are varied as much as 
possible to show different ways of stating a fact with pencil and 
