Strangers visiting the Church of the Ascension, in New York, cannot fail to notice the presence of an old gentleman, who occupies an arm-chair immediately in front of the chancel, in the middle aisle, and who gives the responses to the service in a very loud and distinct manner. This is, perhaps, the oldest man of the entire million of New York city inhabitants. It is Captain Lahrbush, formerly of the British army, but for the last twenty years a New York resident. He was born in London, on the 9th of March, 1765. It is not extravagant to say, that his life has been more remarkable, embracing more various and extraordinary experiences, than that of any one now living, in any quarter of the globe. He entered the military service of Great Britain, October 17, 1789, and fought, under the Duke of York, with the Sixtieth Rifles, in Holland, in the campaign of 1793. Five years later, he was present when Humbert surrendered to Lord Cornwallis, at Pallinauck, in Ireland. In 1801, he was with Lord Nelson at the taking of Copenhagen. In 1806-7, he was an attache of the suite of Lord Castlereagh, at Vienna; and on the 22d of June, of the latter year, he witnessed the memorable interview between Napoleon and Alexander, at Tilsit. During the next two years, he was with the Duke of Wellington, in the Spanish peninsula, and was knighted at Talavera, having received promotion for distinguished gallantry at Busaco. In the year 1811, he was sent to the Cape of Good Hope, and bore a prominent part in the Caffre war of 1813. When Napoleon was imprisoned at St. Helena, Captain Lahrbush was charged with his personal custody, as commander of the guard, a delicate and responsible duty, which he performed for the greater part of 1816-17. The following year, wearying of the military profession, he sold his commission in the Sixtieth Rifles, and retired to private life, but subsequently went to Australia, in the capacity of superintendent of a convict station at Cathure; and in 1837, at the age of seventy-one, removed to Tahiti. From this point he made many voyages, to the East Indies, to China, and to different parts of South America. In 1842, in consequence of having taken sides with the Protestant missionaries against the Roman Catholic propaganda, he was forcibly removed from Tahiti to France, and took occasion of this removal to travel on the continent. In 1847, when eighty-one years of age, he undertook the management of Lord Howard de Welden's estate, in the Island of Jamaica; and, in 1848, came with his widowed daughter and grandson to New York. Both mother and child died soon after their arrival, leaving him, at his advanced age, lonely indeed. But the old man has lived on, to the present moment, in the enjoyment of unimpaired, and a truly wonderful degree of bodily health. In 1867, he celebrated his one hundred and first birthday, at a breakfast in the house of an eminent gentleman of New York, where many officers and citizens were invited to meet him. His appearance is that of a hale man, and, as seen in church, he looks the junior of many others in the congregation. The most surprising fact connected with the old gentleman's prolonged life, is, that for many years he was in the habit of taking seventy-five grains of opium - and, on one occasion, he took one hundred and fifty grains in a dose. Though he has long abandoned the use of the drug, he feels certain he could drink half a pint of laudanum with impunity. Captain Lahrbush is said to retain, with surprising freshness, the scenes and events of some of the grandest and most imposing of modern history of which he has been the eye-witness. He speaks of Blucher as having been very good company, but a heavy drinker, who swore terribly at Napoleon. Louisa, the Queen of Prussia, he thought the handsomest woman of her time, and Alexander, of Russia, the most elegant-looking man in Europe. As for Napoleon, whose face he had an abundant opportunity to study, he declares that no likeness that was ever taken of him, conveys the proper idea of his features and their expression. The closest resemblance, he says, is that of the coins of the empire, especially the profile upon the five franc pieces.