A good reader becomes sooner or later a good book buyer.The sooner,the better. The reading done in a book drawn from a library can not be so pleasant at the moment nor so  permanently useful as the reading done in our own copy.     A book which is worth reading is likely to be read more than once,and at each reading     some idea or some statement makes such an impression that we wish to refer to it again. Some readers underline the page as they read,but I find that a page which I have underlined can not give me so many fresh impressions as one which has no marks on it.My habit is to make my own index of a book as I read.I put down the number of the page and a word or two to identify the thought or the fact which I get from it.On a second or third reading I am likely to double or triple the size of this index.This is my substitute for underlining.Most of the books in my library are so indexed that I can find quickly the passage which from time to time I wish to look up.     To use a book in this way,organizing it for continued usefulness year after year, we     must,of course,do our reading in a copy which belongs to us.The books I buy are chiefly     those of less expensive editions.     As I have grown older and the number of books on my shelves has increased,I appre-    ciate editions which do not take much room.By careful and continuous selection I keep my     librarv down to ten thousand books.This would be,of course,too large a number for any     but a professional scholar or writer.But my advice to a book lover is to weed but his library     at least once every two years,giving away the books which are not likely to be read again.     And never never buy a book which you will not immediately read.A library bought only for     looks is not literature,but indoor decoration. What is the disadvantage of underlining according to the author?
Underlined books look old and not worth reading. The lines make it difficult for the reader to concentrate. Underlined books cannot give the reader enough fresh impressions. The reader cannot find the passage he or she wishes to read again.