Johnson's Physical Book

 'I have just now read  a physical book,' writes Samuel Johnson in 1758, in a letter to his mother. The phrase reads oddly now, as if Johnson had momentarily time-travelled to this digital age when we have to distinguish 'a physical book' from an electronic book, one that exists only on a screen. 
'A physical book' was, in Johnson's day, what we would today call 'a medical book', as becomes clear from the rest of the sentence: 'I have just now read a physical book, which inclines me to think that a strong infusion of the bark would do you good. Do, dear mother, try it.'
Johnson's letters to his ailing mother are touchingly solicitous and tender. As she lay on her deathbed, Johnson had not seen her for nearly 20 years, since his last visit to his native town of Lichfield. This, and the fact that they had never had an easy relationship, no doubt made his sorrow at the prospect of her imminent death all the sharper. His last letter to her reads 
'Dear honoured mother – 
Neither your condition nor your character make it fit for me to say much. You have been the best mother, and I believe the best woman in the world. I thank you for all your indulgence to me, and beg forgiveness for all that I have done ill, and all that I have omitted to do well. God grant you his Holy Spirit, and receive you to everlasting happiness, for Jesus Christ's sake. Amen. Lord Jesus receive your spirit. Amen.
I am, dear mother, your dutiful son,
Sam: Johnson'