16. Letters about which any doubt exists should be carefully weighed before posting. If the Post-Office weight be exceeded to the smallest extent, even to the turning of the scale, a letter becomes liable to, and is charged higher postage--viz. the difference in double or unpaid postage. So trained has the post-office clerk become of late years by a recent system of surcharges, that few letters can now pass with an insufficient number of stamps affixed. To provide against errors in scales, &c. it would be well in all cases to allow a little margin, or ask that the letter be weighed in the post-office scales. In the case of newspapers and book-packets, the same remarks, as well as the same arrangements, apply. It should be particularly remembered that a newspaper when posted, say wet from the printing-office, will often weigh more than it does on delivery; hence surcharges for which the receiver sometimes cannot account. 17. In posting letters, care should be taken to see that they fall into the box, and do not stick in the passage. The pillar-boxes of our towns, whatever may be said to the contrary, are completely safe as a rule, though the same care should be exercised in depositing the letters.[189] 18. The earlier a letter is posted the better in all cases: towards the time for the closing of the letter-box, great haste is indispensably necessary in the manipulations which a town's correspondence must undergo, whilst earlier on it gets carefully disposed of in proper box and bag. When letters or newspapers are posted in great numbers, as in the case of circulars, they should be posted as early as practicable, and should be tied up in bundles with the addresses all in one direction, or they may be delayed in the press of work.[190] 19. Every letter of consequence put into the post should contain the name of the sender and also his address, in order that, if it cannot be delivered as addressed, it may be promptly returned to the writer. 20. All business letters, at any rate, might have the sender's name and address embossed on the back of the envelope. On failure to deliver such letters, they would then be returned to the writers without being opened. Care should be taken, however, not to use envelopes with another person's name embossed in this way, as the letter will be forwarded back to the address thus given, though it should not happen to be the sender's own. 21. Coin is prohibited to be sent in ordinary letters passing between one part of the United Kingdom and another.[191] If a letter be posted containing coin, it will be registered and charged a double registration fee. Coins or any other articles of value, if properly secured, will be certain of careful treatment under the registration system.[192]