After civil war, black people had problems to emancipate still. That's why this period is label as 'another form of slavey'. Because african-american from certain job. In that sense, white people were advantage of this situation, because they were able to hire these people.
The name of the device is the <span>Fessenden oscillator. It was made to allow submarines to communicate through Morse code. This way they could avoid communication being intercepted.</span>
