490 THE POPULAR SCIENCE MONTHLY. 



accuracy tbe time it takes to ^jerceii-^, that is, tlic time passing from 

 the moment at wbich an impression has reached consciousness until the 

 moment at which we know what it is. In my own case about one 

 twentieth of a second is needed to see a white light, one tenth of a 

 second to see a color or picture, one eighth of a second to see a letter, 

 and one seventh of a second to see a word. It takes longer to see a 

 rare word than to see a common one, or a word in a foreign language 

 than one in our native tongue. It even takes longer to see some letters 

 than others. 



The time taken up in choosing a motion, the "will-time," can be 

 measured as well as the time taken up in perceiving. If I do not 

 know which of two colored lights is to be presented, and must lift 

 my right hand if it be red and my left hand if it be blue, I need 

 about one thirteenth of a second to initiate the correct motion. I have 

 also been able to register the sound-waves made in the air by speak- 

 ing, and thus have determined that in order to call up the name be- 

 longing to a printed word I need about one ninth of a second, to a 

 letter one sixth of a second, to a picture one quarter of a second, and 

 to a color one third of a second. A letter can be seen more quickly 

 than a word, but we are so used to reading aloud that the process has 

 become quite automatic, and a word can be read M-ith greater ease 

 and in less time than a letter can be named. The same experiments 

 made on other persons give times differing b\;t little from my own. 

 Mental processes, however, take place more slowly in children, in the 

 aged, and in the uneducated. 



It is possible, further, to measure the time taken up in remem- 

 bering, in forming a judgment, and in the association of ideas. 

 Though familiar with German, I need, on the average, one seventh 

 of a second longer to name an object in that language than in En- 

 glish. I need about one quarter of a second * to translate a word from 

 German into English, and one twentieth of a second longer to trans- 

 late in the reverse direction. This shows that foreign languages take 

 up much time even after they have been learned, and may lead us 

 once more to weigh the gain and loss of a polyglot mental life. It 

 takes about two fifths of a second to call to mind the country in which 

 a well-known town is situated, or the language in which a familiar 

 anchor wrote. AYe can think of the name of next month in half the 

 time we need to think of tlie name of last month. It takes on the 

 average one third of a second to add numbers consisting of one digit, 

 and half a second to multiply them. Such experiments give us con- 

 siderable insight into the mind. Those used to reckoning can add 

 two to three in less time than others ; those familiar with literature 

 can remember more quickly than others that Shakespeare wrote 

 " Hamlet." In the cases which we have just been considering a ques- 



* In all cases the time of association only is given, the time needed to see the one 

 word and name the other having been subtracted. 



