To David Rittenhouse
Paris Nov. 11. 1784.
The news of war inevitable in Europe will interest your philanthropy, otherwise it would scarcely amuse you for me to enter into the details of it as they are likely to arise. I will therefore only tell you in three words that the Emperor and Dutch will take the feild in the spring, and that the former will probably be aided by the Russias, and the latter by France, Prussia and the Porte. England will probably be neuter for the best reason in the world, that she cannot raise money to carry on a war. Ireland too might take the opposite side. I send you the report of the Commissioners on the subject of animal magnetism. You will no doubt have heard of that folly, and perhaps have received this pamphlet. It has actually given a quietus to a madness that was becoming epidemical. You will also receive Roberts account of his last voiage through the air, and a Connoissance des tems for 1785. There is nothing else here lately published worth sending to you. The Abbé Rochon has lately made a very curious discovery in optics. He has made lenses with a chrystal from Iceland which have a double focus, perfectly distinct and at considerable distances from each other. I looked thro’ a telescope to which he had adapted one of these and saw at the same instant an object on the banks of the Seine and a house half a mile further back with equal precision, the intermediate objects being dim as not at a proper distance for either focus. He supposes this chrystal composed of two substances of different refracting powers, not so united as to mingle their effect. He proposes by it a method of deciding in time whether the obliquity of the ecliptic really changes, and he thinks it will be more accurate than those hitherto known. A windmill has lately been announced which unites these advantages. 1. It offers itself to the wind in whatever direction that is. 2. It admits an easy change in the inclination of it’s wings, and may therefore be readily adapted to it’s greater or lesser force. 3. It substitutes wood instead of canvas for the vanes. 4. The geer is all fixed, and not moving on a center as is usual. These are the only improvements in the arts which I recollect at present as worth mention. There are always little things puffed off, but these are not worth notice. Be so good as to present my compliments very respectfully to Mrs. Rittenhouse and the young ladies. Perhaps it will give them satisfaction to know that Patsy is well, and placed to her perfect satisfaction in a convent, tho’ beleive she proposes to write to Miss Hetty, in which case I shall do myself the pleasure of inclosing her letter. Accept yourself assurances of the perfect esteem & respect with which I am Dr. Sir Your friend & Servt.,
MS not found. Text printed from a photostat of RC in PHi. Entry in SJL reads: “Rittenhouse. War in Eur. Send him report Commissioners on Animal magnetism. Roberts last voiage and Conn. des tems 85.”