December 2, 1889.] 



KNOWLEDGE 



33 



working order. This earlier degeneration of later formed 

 .structures is a general fact perfectly familiar to the 

 physiologist." 



One of the most remarkalile features of mental develop- 

 ment, characteristic, according to circumstances, of mental 

 growth and of mental decay, is the change of taste for 

 mental food of various kinds. Everyone must be conscious 

 of the fact that books, and the subjects of thought, lose the 

 interest they once had, making way for others of a different 

 nature. The favourite author whose words we read and 

 re-read with continually fresh enjoyment in youth, appears 

 dull and uninterestmg as the mind grows, and becomes 

 unendurable in advanced years. And this is not merely 

 the effect of familiarity. I knew one who was never tired 

 of reading the works of a famous modern novelist until the 

 age of twenty-five or thereabouts, when it chanced that he 

 was placed in circumstances which caused novel -reading 

 to be an mifrequent occupation, and in point of fact 

 certain works of this author were not opened by him for 

 ten or twelve years. He supposed, when at the end of 

 that time he took up one of these works, that he should 

 find even more than the pleasure he formerly had in 

 readmg it, since the story would now have something of 

 novelty for him ; and he had once thorouglily enjoyed 

 reading it, even when he almost knew the work by heart. 

 But he no longer found the work in the least interesting ; 

 the humour seemed forced, the pathos affected, the elo- 

 quence false ; in short, he had lost his taste for it. In 

 the meantime, the works of another equally famous 

 humourist had iiciuiicd a new value in his estimation.* 

 They had foniu'ii\ ^iiimd rather heavy reading; now, 

 every sentence giixr fiiidviuent. They appeared now as 

 books not to be merely tasted or swallowed, but, as Bacon 

 hath it, " to be chewed and digested." The change here 

 described indicated (in accordance at least with the accepted 

 estimates of the novelist and humourist in (juestion) :in 

 increase of mental power. But a distaste for particular 

 writings may imply the decay of mental power. And also, 

 more generally, a tendency to disparagement is a very 

 common indication of advancing mentrtrl age. " The old 

 brain," says Wendell Holmes, " thinks the world grows 

 worse, as the old retina thmks the eyes of needles and the 

 fractions in the prmted sales of stocks grow smaller." 



Another singular effect of advancing years is shown by 

 the tendency to repetition. It is worthy of notice that this 

 peculiar mental phenomenon has been clearly associated 

 with physical deterioration of the substance of the brain, 

 because it may be brought about by a blow or by disease. 

 Wendell Holmes, speaking of this peculiarity, remarks, " I 

 have known an aged person repeat the same question five, 

 six, or seven times, cbu-ing the same brief visit. I'jvery- 

 body knows the archbishop's flavour of apoplexy in the 

 memory as in the other mental powers. I was once asked 

 to see to a wonum who bad just been injured in the street. 

 On coming to lierself, ' Where am I ".' What has happened "? ' 

 she asked. ' Knocked down by a horse, nui'am ; stunned 

 a little ; that is all.' A pause, while one. with moderate 

 haste, might count a hundred ; and then again, • Where 

 am I '? What has happened ? ' ' Knocked down by a 



* Probably the boBt moans of testing the development of one'.s own 

 mind consiats in comparing the estimate formed, at different times, of 

 the value of some standard work. 0( cunr.'so, diO'crcnt classes of 

 writing should be omployod to test diCferont faculties of the mind. A 

 good general test may h<- funnd in Shakespeare's plays, and perhaps 

 still better in some nf Slml.r .pcMro's sonnets. .\s the mind grows, its 

 power of approciiitiiM. Mi;iki'-.|H;iro increases; and the great advantage 

 of this particular IitI in llial tlii> mind cannot overgrow it. It is like 

 thp standard by whiili the sergeant measures recruits, which will 

 measure men of all heights, not failing even when giants are brought 

 to be measured by it. 



horse, ma'am ; stunned a little ; that is aU.' (Mr. Holmes 

 appears to have sympathised with the patient's condition. ) 

 Another pause, and the same question again ; and so on 

 during the whole time I was by her. The same tendency 

 to repeat a question indefinitely has been observed in 

 returning members of those worshipping assemblies whose 

 favourite hymn is, ' We won't go home till morning.' 

 Is memory, then," he proceeds, " a material record? Is 

 the brain, like the rock of the Binaitic \' alley, written 

 all over with inscriptions left by the long caravans of 

 thought, as they have passed year after year through its 

 mysterious recesses ? When we see a distant railway- 

 train sliding by us in the same line, day after day, we 

 infer the existence of a track which guides it. So, when 

 some dear old friend begms that story we remember so 

 well, switching ofi' at the accustomed pomt of digression ; 

 coming to a dead stop at the puzzling question of chro- 

 nology ; off' the track on the matter of its being first or 

 second cousin of somebody's aunt ; set on it again by the 

 patient, Ustening wife, who knows it all as she knows her 

 well-worn wedding ring — how can we doubt that there is a 

 track laid down for the story in some permanent disposi- 

 tion of the thinking-marrow '? " 



We seem to recognise here a process of change in the 

 brain corresponding to that which takes place in the body 

 with advancing years — the induration of its substance, so 

 that it loses fiexibility, and thus while readily accomplish- 

 ing accustomed work, is not readily adapted for new work. 

 Our old proverb, " You can't teach an old dog new tricks," 

 indicates coarsely enough, but justly, the peculiarity, as 

 well mental as bodily, to which I refer. There is not a 

 loss of power, but a loss of elasticity. We see aged men 

 working well in the routine work to which they have 

 become accustomed, but failing where there is occasion for 

 change either of method or of opinion. Again, one recog- 

 nises this peculiarity in the scientific worker, whence 

 perhaps we may regard it as a fortunate circumstance that 

 the tendency of the aged mmd accords with its facul- 

 ties, so that old men do not readily undertake new work. 

 (To III', amtinufd.) 



PERIODICAL COMETS DUE IN 1890. 



By W. T. Lynn, B.A., F.R.A.S. 



OF the four periodical comets which are expected to 

 return next year, two are of well-estabhshed 

 periods, and have been seen on several occasions ; 

 the other two have each been observed at one 

 rettun, with a probability that it was seen on an 

 occasion several rexolutions earlier. 



Brorsen's was discovered at Kiel on the 2(;th of February 

 IS-iG. Its period is about five and a half years, and it was 

 subsequently observed at returns in 1S57, 1868, 1873, and 

 1879. Another wOl be due early in lf<90. 



D'Arrest's was discovered at Leipzig on the 27th of 

 .Iiuie 1851, it has a period of six and a half years, and was 

 observed in 1857-8, in 1870, and in 1877. It escaped 

 obser\ation in the winter of 1883, but another return 

 will be due next simnner. 



j\I. C'oggia discovered a small comet at Marseilles on the 

 10th November 1873. The investigation of Prof. Weiss " 

 nuidc it probable that this was identical with one detected 

 by Pons on 2:ird February 1818, hut, though its period is 

 probably about live and a half years in duration, it has not 

 been seen since 1873. Returns, if that be the true period, 

 were due in 1879 and 1884 ; and another will be expected 

 to take place early next year. 



