242 ROUGH WAYS MADE SMOOTH. 



his chair, from which he rose now and then, took a volume 

 from the book-case, consulted it, and restored it to the shelf 

 all without intermission in the current of ideas, which con- 

 tinued to be delivered with no less readiness than if his 

 mind had been wholly occupied with the words he was 

 uttering. It soon became apparent to me, however, that he 

 was carrying on two distinct trains of thought, one of which 

 was already arranged and in the act of being spoken, while 

 at the same time he was in advance, considering what was 

 afterwards to be said. 'This I discovered' (he should 

 rather have said, * this I was led to infer ') * by his sometimes 

 introducing a word which was wholly out of place enter- 

 tained instead of denied, for example but which I presently 

 found to belong to the next sentence, perhaps four or five 

 lines further on, which he had been preparing at the very 

 moment when he gave me the words of the one that pre- 

 ceded it.' In the same way I have often unconsciously 

 substituted one word for another in lecturing, the word used 

 always belonging to a later sentence than the word intended 

 to be used. I have noticed also this peculiarity, that when 

 a substitution of this kind has been once made, an effort is 

 required to avoid repeating the mistake, even if it be not 

 repeated quite unconsciously to the end of the discourse. 

 In this way, for example, I once throughout an entire 

 lecture used the word 'heavens' for the word 'screen' 

 (the screen on which lantern pictures were shown). A 

 similar peculiarity may be noticed with written errors. 

 Thus in my treatise on a scientific subject, in which the 

 utmost care had been given to minute points of detail, I 

 once wrote ' seconds ' for ' minutes ' throughout several 

 pages in fact, from the place where first the error was 

 made, to the end of the chapter. (See the first edition 

 of my Transits of Venus, pp. 131-136, noting as an ad- 

 ditional peculiarity that the whole object of the chapter in 

 which this mistake was made was to show how many minutes 

 of difference existed between the occurrence of certain 

 events.) 



