Dear Sir -
I am much obliged to you for your invitation and for the courteous terms in which it is conveyed. I purpose visiting America next year, but whether I shall lecture there or not is as yet undecided. My own preference would be not to lecture, but to pay a friendly visit to a country to which I am indebted for numberless proofs of kindness and appreciation. However, I shall place the decision of this point in the hands of my scientific American friends and be guided by their counsel.
Yours very faithfully