Letter IV. The object of my mission to Argentina was to intal in the National Museum at La Plata a replica of the skeleton of the Diplococus the original of which is in the Carnegie Museum. The replica was given by Mr. Andrew Carnegie to the Republic at the suggestion of President Pena. As I have stated in a previous letter, I was received with the utmost hospitality by the authorities of the Museum and of the University of La Plata. My home during my stay is one of the largest and most finest equipped institutions of its kind in South America. A very large sum of money has been expended by the Government in erecting buildings and securing instruments, but unfortunately up to the present time the sceientific results achieved, in spite of the fine equipment of the institution, have not been comparable with those acheived at some other point where less money has been available. To remedy this condition of affairs, with great wisdom the authorities have invited to the Directorship of the institution that admirable astronomer, Professor Hussey, whose work at the Observatory at Ann Arbor in Michigan is known to all men of science. I desire to acknowledge the courtesy and warm hospitality of the genial Director and his associates. I was received with cordiality by the President of the Republic, to whom I has the honor of being presented by the Hon. John W. Garrett, the genial and most efficient representative of our Government.