Bell and his assistant Charles Sumner Tainter jointly invented a wireless telephone, named a photophone, which allowed for the transmission of both sounds and normal human conversations on a beam of light. Both men later became full associates in the Volta Laboratory Association.
বেলের কর্ড-ফ্রি ফোন বার্তা প্রেরণ করার জন্য কী ব্যবহার করেছিল?
light