156 ANNUAL OF SCIENTIFIC DISCOVERY. 



increased, and a considerable current obtained from the other 

 wire for external work ; or, there might be two armatures, one to 

 increase the power of the magnets, and the other for blasting or 

 other purposes. Two bars of soft iron, 7^ X 2 X h inches, are 

 c'.ich wound round the centre portions with about 30 yards of No. 

 10 copper wire, and shoes of soft iron so attached at each end that 

 when the bars are placed one above the other, there will be a 

 space left between the opposite shoes in which a Siemens arma- 

 ture can rotate. On each of the armatures is wound about 10 

 yards of No. 14 copper wire, cotton-covered. If the armature, in 

 connection with the electro-magnet, is made to rotate, there will 

 be a very feeble current generated in it ; this passing round the 

 electro-magnet will increase its power with every additional im- 

 pulse. It will thus be seen that the only limit to the power of the 

 machine is the rapidity with which the armature is made to ro- 

 tate, which is entirely dependent on the amount of dynamic force 

 employed. The great improvement in this machine is the intro- 

 duction of the second armature, which, although it takes off cur- 

 rents generated in its wire by the increased magnetism, does not 

 at all interfere with the primary current, and, when attached to a 

 regulator, is found to give an electric light equal to 40 elements 

 of Grovel or Bunsen's at the expenditure of one horse-power. 



He exhibited a machine at the Paris Exposition about 24 inches 

 in -length, 12 inches in width, and 7 inches high. Though imper- 

 fectly constructed, its power would keep 50 inches of platinum 

 wire, .01 in diameter, incandescent, and when a small voltameter 

 was placed in circuit with the second armature, it would give off 

 250 cubic centimetres of gas per minute. Quart. Jour, of 

 Science, 1867. 



PROF. WHEATSTONE'S. CRYPTOGRAPH. 



The importance of a secure cipher for commercial, military, 

 and other telegrams of a confidential nature, grows with every 

 step in the extension of telegraphic correspondence, and has 

 brought forth a most ingeniously simple and effective invention 

 for the purpose mentioned, which has been adopted by the British 

 War Office. The parties to a confidential correspondence by tele- 

 graph are each furnished with a little instrument consisting of a 

 dial having the letters of the alphabet printed in regular order 

 in a circle near the circumference, with one blank space, making 

 27 intervals. In a circle within this runs a flanged groove having 

 room for just 26 letters, and in which the letters, printed on sep- 

 arate bits of card of the exact size, are arranged in any arbitrary 

 order understood between the parties. A secure and convenient 

 way to fix this arbitrary order in the mind without risking it on 

 paper, is to agree upon any word easily remembered, and when 

 a despatch is to be sent or deciphered, write down the letters of 

 this word, and under them write the remaining letters of the 

 alphabet in their proper order from right to left, one letter under 

 each letter of the word, then beginning another line under this in 

 the same way, and so on until the entire alphabet is arranged in 



