When you did me the honour to mention, the other day, the doubts you entertained concerning the correctness of the ordinary recieved opinions touching the effect of the latteral pressure of fluids acting on the interior of a leading main-pipe, I hesitated to give an immediate answer as to what instances (if any) had occurred to me, in a practical case, where the operation had been risqued beyond the customary calculated balance of the Atmospheric column. But, as your impressions in this matter (at least, in the way I understood them) appeared to me to assume too much to be tried at the risk of your reputation, (allowing to you the rank which cotemporaries have ascribed to you as one of the Fathers of Philosophy) I began to reflect, after you had left us, on the pitch of the several lines of lead I had run in and near the City of London; in order to confine the absolute pressure on various Mains, belonging to different water works, to some degree of precision.—I find, in remembrance, that, I either possess by recollection or the actual document, materials enough to form the basis of satisfactory conclusions; and, if you will favor me with a sectional Clue of Your premises, shewing (as near as you can guess) the Spring head, the lowest bend in the valley, & the point of re-elevated discharge at which you wish to convert your water to domestic, Culinary, or Horticultural purposes, I have no doubt I shall be able to throw a satisfactory light on your proposition, and to furnish you with a drawing of simple works which I am persuaded you will be pleased with.

I have the honor to be Dr. Sir Your sincere friend & H. Servt