NATURAL PHILOSOPHY. 157 



botli lines and columns, which are to be read vertically, and the 

 letters in the inner circle of the dial are to be arranged in that 

 order. After the despatch is sent or deciphered, as the case may 

 be, remove the letters, and the instrument is again uncommuni- 

 cative. 



But the mode of communication remains to be described. The 

 centre of the dial is penetrated, exactly like a clock, by a shaft or 

 arbor passing through a hollow arbor, the former bearing a long 

 and the latter a short index hand. Each of these arbors has also 

 fixed on it a spur-wheel, gearing on a loose pinion common to both, 

 so that turning the one turns the other. But the spur-wheel of the 

 short hand has 26 teeth and that of the long hand 27, answering 

 respectively to the divisions of the inner and outer circles, so 

 that at every revolution of the long hand, the short hand com- 

 pletes the circuit of the alphabet and one letter further, thus 

 gaining one every time. Consequently, a message spelled out 

 with the long hand, and written out in the letters simultaneously 

 indicated by the short hand, would be in a constantly changing 

 cipher, in which no letter would be represented twice by the same 

 substitute, and no possible clue could be obtained without first ob- 

 taining the magic word upon which the inner circle of letters was 

 arranged. The receiver of the message, having properly ar- 

 ranged the arbitrary alphabet in the instrument, has only to turn 

 the short hand to the letters of the despatch as received, in suc- 

 cession, and write off those indicated by the long hand. The in- 

 strument is, of course, only to be turned forward, or from left to 

 right. Scientific American. 



ELECTRIC-DISTANCE METER. 



The collection of articles sent to the Paris Exhibition by the 

 Austrian War Office contains an ingenious apparatus, invented by 

 M. C. Cocziczka, captain in the corps of engineers, for measuring 

 the distances and indicating the movements of distant objects. 

 This apparatus requires two points of observation placed at a cer- 

 tain measured distance from each other, and connected by a tele- 

 graph wire. At each of these stations a telescope is used for ob- 

 serving the object in view, and below the telescope a small table 

 is placed in one of the stations, representing the map of the space 

 in front of the observer. At one fixed point upon the table, ex- 

 actly below the axis of the telescope, there is a long thin needle 

 balanced upon a point, and connected to the telescope, so as to 

 follow all movements of the latter and to be always parallel to its 

 line of sight. 



Beside this, a second needle, which turns round a point which 

 represents the second point of observation upon the small map, is 

 placed upon the table, and this second needle is connected with 

 the telescope of the other station by an electric arrangement. 

 The movement of the distant telescope is made to cause this nee- 

 dle to turn to an equal angle with itself, in a somewhat similar 

 manner to the magnetic needles of the electric telegraph. The 

 distance between the centres of the two needles on the paper 



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