There is also the fatal invention of the General Delivery.  A lover finds in the world a hundred charitable persons, male and female, who, for a slight consideration, will slip the billets-doux into the amorous and intelligent hand of his fair mistress.

A correspondence is a variable as Proteus.  There are sympathetic inks.  A young celibate has told us in confidence that he has written a letter on the fly-leaf of a new book, which, when the husband asked for it of the bookseller, reached the hands of his mistress, who had been prepared the evening before for this charming article.

A woman in love, who fears her husband’s jealousy, will write and read billets-doux during the time consecrated to those mysterious occupations during which the most tyrannical husband must leave her alone.

Moreover, all lovers have the art of arranging a special code of signals, whose arbitrary import it is difficult to understand.  At a ball, a flower placed in some odd way in the hair; at the theatre, a pocket handkerchief unfolded on the front of the box; rubbing the nose, wearing a belt of a particular color, putting the hat on one side, wearing one dress oftener than another, singing a certain song in a concert or touching certain notes on the piano; fixing the eyes on a point agreed; everything, in fact, from the hurdy-gurdy which passes your windows and goes away if you open the shutter, to the newspaper announcement of a horse for sale—­all may be reckoned as correspondence.

How many times, in short, will a wife craftily ask her husband to do such and such commission for her, to go to such and such a shop or house, having previously informed her lover that your presence at such or such a place means yes or no?

On this point the professor acknowledges with shame that there is no possible means of preventing correspondence between lovers.  But a little machiavelism on the part of the husband will be much more likely to remedy the difficulty than any coercive measures.

An agreement, which should be kept sacred between married people, is their solemn oath that they will respect each other’s sealed letters.  Clever is the husband who makes this pledge on his wedding-day and is able to keep it conscientiously.

In giving your wife unrestrained liberty to write and to receive letters, you will be enabled to discern the moment she begins to correspond with a lover.

But suppose your wife distrusts you and covers with impenetrable clouds the means she takes to conceal from you her correspondence.  Is it not then time to display that intellectual power with which we armed you in our Meditation entitled Of the Custom House?  The man who does not see when his wife writes to her lover, and when she receives an answer, is a failure as a husband.

The proposed study which you ought to bestow upon the movements, the actions, the gestures, the looks of your wife, will be perhaps troublesome and wearying, but it will not last long; the only point is to discover when your wife and her lover correspond and in what way.