Another trick is to have an answer appear written upon the inside of the body of the envelope in which is enclosed the question. The envelope is closed and sealed with sealing wax. This is accomplished without disturbing the seal. In the ordinary manufacture of an envelope, three of the flaps are stuck together with adhesive gum of far less strength than the fourth flap, which is to be moistened and closed by the user. It is generally an easy matter to insert the blade of a penknife behind the bottom flap, that is, between it and one of the end flaps, and separate them a trifle. Then, if you insert into this a wooden skewer, or hard, round-pointed stick, like a pencil, in fact, a lead pencil will do, but look out it does not leave marks behind; and by pushing this along, and giving it a rolling motion, you will separate the flaps up as far as the seal, and, if done carefully, without tearing or mutilating the envelope. Now, on a slip of paper write the answer or suitable message, but in reverse or backward writing, as the words would appear in a looking-glass, with a carbon or copying pencil. Pass this slip through the opening in the envelope, shake it into the desired position, now rub the envelope over this spot until you think the envelope has taken the impression. Then remove the slip of paper by the same way it came in, moisten and gum the opening, and the trick is done. In rubbing the envelope, it is a good plan to place a piece of paper over it to keep the envelope clean of marks, which would be liable to appear from damp or moist fingers during the rubbing. The following is from the experiments of a German scientist. He discovered, by the use of an embryoscope, or egg-glass, that the shells of eggs were of very unequal thickness. It occurred to him to make experiments in order to ascertain how many leaves of ordinary letter or official paper must be laid above and below a written leaf, in order to make it illegible to a highly sensitive eye in the direct sunlight. He found that after he had rested his eye in a dark room for ten or fifteen minutes, he could read a piece of writing over the mirror of the embryoscope that had been covered with eight layers of paper. He called in other observers to confirm this. The letters, however, that could be thus deciphered were written in dark ink on one side of the paper only. If four written sides were folded together, and especially if there had been crossing, it was hard to make out the drift of the writing; and there are some kinds of writing which, when folded thrice or twice, admit too little light for the purpose of decipherment. In this way, possibly, many of the performances of “clairvoyants” may be explained. By means of the egg-glass it is, as a rule, easier to make out the contents of a letter or telegram without the slightest tampering with the envelope than it is to detect the movements of the embryo in the egg.