source A New System of Sound Recording by HC Harrison Bell Laboratories Record Vol10 No 11 July 1932 p392
横溝記録と縦溝記録の比較音溝の振幅が大きくなっても縦溝の場合高密度で記録可能であることを説明する図版
comparison of lateral vertical cuts showing the vertical cut with high density
Fig.3 – The waves cut by the new method are in a vertical rather than a horizontal plane (Harrison, 1932)