This belief in the visits of domestic spirits, who busy themselves at night in sweeping and arranging the lower apartments, has prevailed in the North of Ireland and in Scotland from time immemorial: and it is explained in SIR WALTER SCOTT'S notes to the _Lay of the Last Minstrel_, as his justification for introducing the goblin page Gilpin Horner amongst the domestics of Branksome Hall. Perhaps, from the association of these elves with the lower household duties, but more probably from a more obvious cause, came at a later period the practice described by GIFFORD in his note on BEN JONSON, as quoted by your correspondent (Vol. ii., p. 170.), by which-- "in all great houses, but particularly in the Royal Residences, there were a number of mean dirty dependents, whose office it was to attend the wool-yard, sculleries, &c. Of these, the most forlorn wretches seem to have been selected to carry coals to the kitchens, halls, &c. To this smutty regiment, who attended the progresses, and rode in the carts with the pots and kettles, the people, in derision, gave the name of the _black guards_." This is no doubt correct; and hence the expression of BEAUMONT and FLETCHER, quoted from the _Elder Brother_, that-- "... from the _black guard_ To the grim Sir in office, there are few Hold other tenets:" meaning from the lowest domestic to the highest functionary of a household. This too explains the force of the allusion, in Jardine's _Criminal Trials_, to the apartments of Euston House being "far unmeet for her Highness, but fitter for the Black Guard"--that is, for the scullions and lowest servants of an establishment. SWIFT employs the word in this sense when he says, in the extract quoted by Dr. Johnson in his _Dictionary_ in illustration of the meaning of _blackguard_,-- "Let a black-guard boy be always about the house to send on your errands, and go to market for you on rainy days." It will thus be seen, that of the six authors quoted in "N. & Q." no one makes use of the term _black guard_ in an opprobrious sense such as attaches to the more modern word "blackguard;" and that they all wrote within the first fifty years of the seventeenth century. It must therefore be subsequent not only to that date, but to the reign of Queen Anne, that we are to look for its general acceptance in its present contumelious sense. And I believe that its introduction may be traced to a recent period, and to a much more simple derivation than that investigated by your correspondents.