WHY Londoners should presume to sneer at the morality of the volatile Parisians, has always been a sore puzzle to me. During the past fifteen years, sharp observers of society in the English Capital have been appalled by the visible and marked progress of moral and social deterioration among the people who affect to give tone, and breeding, and refinement, to all that they do or say, as leaders of society. Polite London Society has always plumed itself upon being superior, in a moral sense, to the corresponding class in the French Capital, but it must strike those who have held such views, that there is no basis for the belief any longer, when the notorious fact is offered to them, that two of the highest personages in England are men who lead lives of immorality--I refer to the Prince of Wales and the Duke of Cambridge. I have however said enough of those two loose gentlemen, and I shall proceed to consider the subject in its larger bearings. I boldly assert, that English Society, of the highest class, is to-day as rotten in every sense, as were the French nobility, with their mistresses and their "little establishments," before the whirlwind of the Revolution of 1793 swept away all that was of hideous corruption and infamy, never to rise again. The proudest names among the English nobility are those which have some moral or dishonorable taint affixed to their titles, by their conduct in life. [Sidenote: MISS HARRIET MONCRIEFFE.] Many of my readers must recollect the termination of the famous Mordaunt case, in which the Prince of Wales was implicated, and it will also be remembered that the few facts which were developed on the trial, despite the attempt of Lord Penzance, (acting under pressure of the Throne,) to hush them up, had the effect of shaking England to the centre, socially speaking. Miss Harriet Sarah Moncrieffe, now Lady Mordaunt, is a daughter of Sir Thomas Moncrieffe, a baronet of one of the oldest families in Scotland. The family seat is at Earn, in Perthshire, and the mansion and grounds are among the finest in North Britain. The family was a large one, four sons and six daughters being born to Sir Thomas and his wife, who was a daughter of the Earl of Kinnoul. Lady Harriet's eldest sister is married to the Duke of Athole, one of the richest and most powerful of the Scotch nobles. Then she has a sister married to the Earl of Dudley, and another to a Mr. Forbes, of a wealthy Scotch family, into which, if I be not mistaken, Lady Douglas-Hamilton, a sister of the Duke of Hamilton, is married. One of the sisters--the Duchess of Athole, has for her mother-in-law the Dowager-Duchess of Athole--who is a tried and trusted friend of Queen Victoria, being, as I believe, a Lady-in-waiting, or a Lady-of-the-bed-chamber to the Queen, or something of that sort. Altogether the family and its connections are among the very thickest cream of English aristocratic society.