Some inconvenience arose at first, and probably is still experienced in a less degree, from the greater opportunity for mischief afforded by these isolated boxes, though there is some set-off in the circumstance that the most wanton or malicious act directed against them can extend no further than to the boxes and their contents. An abominable attempt, made in the year 1859, to set fire during the night to the contents of a box at a post office--that of Devonport--besides partially effecting this detestable purpose, greatly imperilled the whole building, and even placed in jeopardy the lives of the postmaster and his family.[182] NUMBER OF LETTERS. The increase in the number of chargeable letters delivered in the United Kingdom was from 443 millions in 1854[183] to 545 millions in 1859;[184] _i.e._, from somewhat less than six-fold of the number previously to the establishment of penny postage to somewhat more than seven-fold; so that the mere increment during these five years far exceeds the total amount under the old rates; the one being 102 millions and the other only 76 millions.[185] RETURNED LETTERS. In the Report for 1855 there is striking information as to reduction in the proportion of returned, mis-sent, and redirected letters which followed the establishment of penny postage. In the year 1838 the postage so lost amounted to 4-1/4 per cent. on the gross postal revenue of Great Britain. In three years it had fallen to 2-1/4 per cent., in eleven years more to 1 per cent., and in three years more to 3/4 per cent.;[186] and the proportion seems to have fallen afterwards still lower.[187] REGISTRATION.