“Well, after each letter, we will write in order the letters in the alphabet that follow it. After A we will write B C D E F G, and after L we will write M N O P Q R, and whenever we get to Z we start the alphabet again. So if we write our whole names it will look like this-- A. B C D E F G L. M N O P Q R I. J K L M N O N. O P Q R S T E. F G H I J K G. H I J K L M I. J K L M N O L. M N O P Q R L. M N O P Q R E. F G H I J K S. T U V W X Y P. Q R S T U V I. J K L M N O E. F G H I J K I. J K L M N O A. B C D E F G N. O P Q R S T M. N O P Q R S E. F G H I J K N. O P Q R S T S. T U V W X Y T. U V W X Y Z R. S T U V W X I. J K L M N O E. F G H I J K Now there are 25 letters in each column, and if we just put a number at the top of our communication, we shall know where we are to begin to use the sequence.” “I see,” said Aline, “if the number is 51 we shall begin at the top of the third column; if it is 56 we shall begin 6 letters down the third column.” “And if it was 176,” said Ian, “what should we do?” “Well, we should have to make another column the same way and we should begin at the top of it.” “Now suppose the number is 1, we shall then begin at the very beginning, and the way we should use the letters would be like this. Suppose this is the message,-- “Arthur Melland wishes to notifie the good people in the Lothians of the lasting excellence of his wares. His pack is regularly filled with all the newest materials and, too, all is most marvellously finished in design. Our first letter was A, and the first A we find is the A of ‘Arthur.’ Our second letter was L, and the next L that we find is in ‘Melland.’ Our third letter was I and the next I that we find is in ‘wishes.’ Our fourth letter was N and the next N that we find is in ‘notifie.’” “Oh, that’s quite easy,” said Aline, “and so you mark them all like this-- “_A_rthur Me_l_land w_i_shes to _n_otifi_e_ the _g_ood people _i_n the _L_othians of the _l_asting _e_xcellence of hi_s_ wares. His _p_ack _i_s r_e_gularly f_i_lled with _a_ll the _n_ewest _m_at_e_rials a_n_d, too, all i_s_ mos_t_ ma_r_vellously f_i_nished in d_e_sign. and then cut them out.” “Yes,” said Ian, “and the only other thing necessary is that the paper should first be neatly ruled with quarter inch squares, and each of the key letters carefully written in a square. It does not matter about the others. But then when the receiver gets the letter he knows that the squares to be cut must be exactly an even number of quarter inches from the edge of the paper.” “I hope I shall remember it if needful,” Aline said. “I don’t,” said Audry.