A lady-help does not like to undertake this office, and to the mistress it appears still more unsuitable. But let us analyze the subject. There are four classes of people who knock at our door: the family, tradespeople, visitors, and casuals. The first division of the difficulty may be easily disposed of. The master and mistress, for these titles must be strictly maintained, have each a latch key; the rest of the family may habitually use a particular knock agreed upon between them, and then the person who happens to be nearest to the door will open it. Schoolboys and girls return at stated hours, and one is prepared for their appeal. For several years past my family has used four single knocks, which is a sign sufficiently unlike other knocks to be recognized immediately. The postman's knock is well known, and in families where there is no great eagerness to get the letters, they fall naturally into the letter-box, which should be made deep, and the slit large enough to admit the _Times_ newspaper easily. In Italy it is usual to write the word _fuori_ on a card, and stick it in the door when one is not at home; and in this case visiting-cards would also be left in the letter-box. We might adopt this method, or even the Temple fashion of saying when we are likely to be home again. The tradesmen are the most difficult to arrange for, and here invention must be called into play. Tradespeople first call for orders, and then with supplies. Suppose we had our doors fitted with a kind of turnstile door, something like the birdcage gates which used to be at the Zoological Gardens, only with the outside made of wood, closely fitting, so as to admit no draught. This, by a push, would allow the goods to be deposited within the door, on the table upon which the cage turns round. The opening should be of a size to admit a leg of mutton easily. The goods, once deposited, could not be removed from the outside, as the door only works one way. Through this opening the lady-housekeeper might give her own orders without their interpretation by an underling, and without being exposed to the public gaze, as she would be if the front door were fully opened, while the leg-of-mutton aperture would be sufficient for both parties to see to whom they were speaking. In the case of a single door, instead of the very general folding doors, it would be necessary to have the cage made to fold back, and the table to let down with hinges, to allow of the door being opened back against the wall; the table might be lowered after midday. This arrangement would also dispose of most of the casuals--the beggars, pedlars, and others who haunt our door-steps--to the entire prevention of hall robberies.