OVERBOARD IN MIDOCEAN STRANGE DISAPPEARANCE OF GEN. J. H. VAN ALEN. LOST ON THE VOYAGE FROM LIVER- POOL TO NEW-YORK--HIS DEATH BELIEVED TO BE ACCIDENTAL. Among the passengers of the Cunard steam- ship Umbria, which sailed from Liverpool for New-York on July 17, were Gen. J. H. Van Alen, of New-York, and his brother-in-law, Mr. R. F. Grinnell. When the General's only son went to the Cunard pier yesterday to welcome his father, upon Mr. Grinnell devolved the duty of telling him that Gen. Van Alen had disappeared from the steamship in midocean three days before. Gen. Van Alen had sailed from this country only about five weeks ago in order to place his grand- children in a private school, near Southampton, and was returning, with his brother-in-law, to his son's home in Newport. Mr. Grinnell was so much prostrated by the affair that it was with an effort that he gave such details as he knew. He was positive that Gen. Van Alen's disappear- ance was due to an accident, and not to an in- tention of ending his life. Gen. Van Alen, he said to a reporter of of THE TIMES at the Westminster Hotel last evening, had for several weeks been suffering severely from dysentery, which became much worse on shipboard. They had engaged the Cap- tain's stateroom, and Gen. Van Alen was closely confined to it from the time the ship sailed until the day he was lost overboard, never leaving it except with the assistance of his companion. Mr. Grinnell kept a memorandum during the voyage of the changes in Gen. Van Alen's condi- tion. An entry made at 10 P. M. on Wednesday, July 21, speaks of the General as being much ex- cited and unable to sleep. Mr. Grinnell sat up with him in the hope that he might become more quiet. The next entry is at 1 A. M. Thursday morning. The sick man had just awakened from a short sleep, said he felt better, and urged Mr. grinnell to take some rest. Mr. Grinnell kept awake, however, until nearly 3 o'clock on Thursday morning, and then, as Gen. Van Alen seemed resting quietly, Mr. Grinnell himself lay down on a sofa opposite and fell into a light sleep. He awoke an hour later, and look- ing toward the sofa on which Gen. Van Alen had been sleeping he was startled to see that he was not there. Hurriedly rushing on deck he aroused the Cap- tain and his room steward, and the three searched the vessel in every part, but the missing man could not be found. Later in the day the third officer told the Captain that about 4 o'clock he had noticed a cabin passenger on the extreme aft deck, but had paid no particular attention to him, as it was a common thing for passengers to be seen there at all hours. Mr. Grinnell has no doubt that this passenger was Gen. Van Alen, who for some purpose had left his cabin without arous- ing his companion. Aside from all other reasons which go to prove that the death of Gen. Van Alen was accidental Mr. Grinnell says that in his exhausted state he could have never have climbed over the rail so as to have thrown himself over- board. The weather at the time was very rough for this season, and a strong head wind was blowing, causing the vessel to pitch considerably for one of her size, and his belief is that the General, leaning over the rail and per- haps steadying himself with his stick, lost his balance in a sudden lurch of the vessel and was unable to save himself. Gen. Van Alen was the only son of James T. Van Alen, who was born in Columbia County, and was well known as one of the most successful of the old merchants of New-York. The family is of the old Dutch or "Knickerbocker" stock, and on his mother's side Gen. Van Alen was re- lated to the Trumbulls of Connecticut. The General was about 70 years old. During the early part of his manhood he was in business with his father. When the war broke out he raised and equipped a regiment, and joined the Army of the Potomac. He rose to the rank of a Brigadier-General, and was Gen. Hooker's Chief of Staff at the battle of Chancellorsville. His brother-in-law, Mr. Grin- nell, fought on the Confederate side. The Gen- eral's wife died some years ago. His son and only surviving child, James Van Alen, married a daughter of William Astor, of this city, and lives at Newport. Gen. Van Alen came into prominence in poli- tics after the Presidential election of 1876, when President Grant appointed him as one of the visiting statesmen to Louisiana. He was a Re- publican. On Jan. 3, 1877, after his return from New-Orleans, he delivered an address before the Political Reform Club, in this city, on "The Vote of Louisiana," which attracted considerable at- tention.