Popular Science Montlihj 



;-^a. 



inn ill miml)i'r with thost- of the miiie- 

 tifld units. Hchind each .sf|uaro a lamp 

 i^ mounted. As a hostile ship [)asse.s 

 ihroutjli a mine-field the nearest micro- 

 phones pick up the \il)rations ot her 

 propellers and the corresponding l<uiip> 

 on the board glow. The luminous 

 annunciator may be twenty or more 

 miles distant from the microphones; 

 it may be in 

 Chicago and 

 the m i n e - 

 field in New 

 York Harbor, 

 if there were 

 any military 

 advantage in 

 that great 

 separation. 

 It is always 

 possible to 

 follow the 

 course of an 

 intruding \'es- 

 sel merely bj- 

 watching the 

 lights as they 

 flare up and 

 die out in the 

 squares of the 

 1 u m i n o u 3 

 a n n u n c i a t o r . 

 The lamps ac- 

 tually \isualize 

 the course tak- 

 e n b >■ the 

 vessel under 

 observation . 

 If she enters 

 square 2 2 o f 

 the field the 

 lamp behind 

 square 22 on 

 the annuncia- 

 tor boanl 

 glows ; as she 



slips into square 2:1, of the mine-field, 

 lamp 22 is extinguished and lamp 2.^ 

 Hares up. The accompaiu"ing diagram 

 will explain the general principle. 



Mines are expensi\-e. To provide 

 them with microphones and to wire the 

 microphones to a luminous annunciator 

 board adds to the cost of the installation. 

 Suppose that it were possible to use 

 fewer mines, in other words, to use 

 rather large squares, and suppose that 









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-"MINE ^-'MINE 



OlASRAMOr MINEflELi) UNIT 



The mines, provided with microphones to hear the 

 vibrations of ships which seek to enter a harbor, are 

 arranged in numbered squares. A luminous indicator 

 on shore, marked off into squares corresponding in num- 

 ber with those of the mines is electrically connected 

 with the microphones. Each mine-square is represented 

 on the indicator by a lamp, which glows in its 

 proper square on the luminous board as soon as a hos- 

 tile ship enters and is heard. Thus it is possible to 

 follow by the successive flaring up of lamps the course 

 of a submarine or battleship threading its way thrQugh 

 the mine-field and to explode the right mine 



it were possible \n rlelermine nol merely 

 the |)articular s(|uare into which ;i 

 hostile \essel has found its way but 

 the particular mine of that sf|uare 

 nearest w hich it happens to be -wouUI 

 not that soke the problem of cheapening 

 the installation and heightening its 

 effectixeness.-" 



With this idea in mind I have connec- 

 ted with the 

 I u 111 i n o u s 

 an n u ncia tor 

 board what 

 ma>' be <;dli-il 

 a "|)recisif>n 

 indicator," the 

 () n r pos e o f 

 which is to 

 show which 

 mine is to be 

 explrided in 

 order to des- 

 tro\- llu' inter- 

 loper. A single 

 precision iufji- 

 calur scrvt's 

 for all tjie 

 mines; f i> r 

 the wiring /is 

 such that the 

 precision 

 indicator can 

 be switched 

 into the circuit 

 of any mino- 

 s(|uare at will. 

 The details 

 cannot bo 

 re\'ealed at the 

 I)rescnt time, 

 because they 

 are the subject 

 of a patent 

 application 

 awaiting 

 official action. 

 It nui\- be stated, however, that the 

 de\ ices emplo\ed accurately locate a 

 \essel in a s(|uare by averaging the 

 momentary,- respf)nsi\eness of the four 

 microphones at the corners of the sc|uare. 

 It is very much as if a pencil were attach- 

 ed by four cords tfj as man\' (lulling 

 devices, the pull on each cord coming 

 from a different jxiint of the rompa.ss and 

 representing the intt'iisity of the sound 

 heard in a microphone. Pulleil in alt 



