My dear boy, I have some advice for you; I do hope that you will take it as it is intended--as from an old friend and tutor who wishes you only well. It has come to my attention that you are--shall we say--prostituting your talents. A friend of mine who works at the War Office tells me that you are doing some mathematical work by correspondence--something to do with cannon, I believe. Now, I quite understand that you are in a somewhat precarious financial position, and believe me, I deeply sympathise with you. I know that the earning of a few pounds can mean a great deal to you in furthering your education. I do not say that such work is menial, either. I would not have you think that I deplore your choice of work in any way; it is necessary work, and money is certainly necessary for life. However, let me warn you: a simple task like this, which pays rather well, can become soporific in its effect. Many men of talent, finding themselves comfortably fixed in a mediocre position, have found their minds have become stultified through long disuse. _Please_, dear boy, don't fall into that trap; don't throw away a fine career in mathematics for the sake of a few paltry pounds. You are young and inexperienced, I know, and have a great deal yet to learn, so please take the advice of one who is somewhat older and wiser. No, I haven't gotten round to reading your paper yet; I'll do it this evening, my boy, I promise. Most sincerely, Isaac Barrow * * * * * 3 January 1667 Cambridge My dear Isaac, I read your paper, and I am, I must confess, somewhat nonplussed. What _are_ you doing? I see that my letter of yesterday was somewhat premature; I should have waited until I had read your paper, since it is in exactly the same category. You ask: "What is the optimum shape for a wine barrel? Should it be tall and thin, or squat and broad?" And I ask: "What on Earth difference does it make?" Surely you are not thinking of becoming a wine merchant? If so, what need is there to waste your time studying mathematics? On the other hand, if you intend to become a mathematician, why should you debase a noble and lofty study by applying it to wine barrels? As I told you, I have no objection to your making a few pounds by doing minor calculations for the Army, but this is foolishness. You have gone to a great deal of trouble for nothing; as you gain more experience, you will realize the folly of such things.