604 Mr. diaries Mercier [May 3, 



the right below, a stretch of blue water ; below on the left a con- 

 fused mass of buildings, without specific shape or colour ; dark 

 foliage somewhere between this and the mountain. All the details, — 

 the boats, the moving people, the traffic in the streets, the specific 

 shapes and spatial relations of objects, — all are gone, and all went, 

 not simultaneously, but by gradual and successive effacement. So 

 that we infer that over the disturbed area the disturbance varies 

 much in degree, for the endurance of the set depends, as far as we 

 know, upon its initial extent only. 



Upon what then does the amount of the set depend, and what are 

 the factors that determine it? We can scarcely be wrong in supposing 

 that in this, as in other cases, the distortion produced in a body is 

 dii"ectly proportional to the amount of the incident motion, and in 

 inverse proportion to the inertia of the particles of the body — to the 

 resistance which they oppose to distortion. The first factor need not 

 be laboured. We all know that the stronger the impression made 

 upon us, the longer and the more faithfully it is remembered. Our 

 ancestors, when they took the schoolboys to the boundary of the 

 parish and there flogged them, were quite aware that a strong im- 

 pression produces an enduring memory ; and the whole experience 

 of our lives testifies to the truth of the statement. But something 

 needs to be said about the second factor in the endurance of a memory, 

 viz. the inertia of the tissue on which the motion is incident. 



It is manifest from our daily experience that the inertia of the 

 particles of nervous tissue differs immensely not only in different 

 people, but in different regions of the same brain. We see constantly 

 that the same experience which will produce an enduring set in the 

 brain of one man will not shift the molecules of another beyond the 

 elastic limit. One man will remember and repeat verbatim a leading 

 article in the 'Times' after once reading, while it will take another 

 half-an-hour to learn the Collect for the day. And in the same brain 

 there are differences as wide. The same man who can repeat his 

 leading article after a single reading is unable to recall the simple 

 succession of musical notes that make up some popular tune, even 

 after he has heard them a dozen times. But the man who can re- 

 member one verbal composition can remember another, and he who 

 can remember one musical air, or one set of muscular adjustments, 

 can remember another. We must admit, therefore, that there is in 

 certain individual tracts of brain tissue a specific degree of inertia, 

 but that this degree of inertia differs much, not only in different 

 brains, but in different parts of the same brain. The great practical 

 question for us is whether this inertia can be in any way diminished ; 

 whether there are any means that we can employ by which we can 

 increase the amount of set that is produced without increasing the 

 intensity of the impression which produces it. Undoubtedly there 

 are such means, but before I state them let me deprecate the notion 

 that there is any royal road to the production of what is called a good 

 memory. The ability to remember may be vastly, indefinitely im- 



