IN the variable width method of recording sound on film, a galvanometer is used in which a loop of metal ribbon, 0-005 in. broad and 0-0005 in. thick, is placed between the poles of a permanent magnet ...

ATTENTION has recently been drawn more than once (notably by Sir William Thomson, and by Mr. W. H. Preece and Mr. Kemp) to the advantages offered, in certain cases of the use of the ...