Glass specific gravity hydrometer by J W Towers
1920-1960
1920-1960
1930-1960
1930-1960
1871
2013
1920-1930
1943
1960-1970
1920-1960
1900-1980
1920- 1960
1920-1960
1920-1960
1920-1960
1920-1960
1920-1950
1880-1910
1920-1960
1900-1980
1960-1970
1981
1920-1960
1980-1988
1920-1950
1920-1960
1938
1960-1975