Unconvertible

I can only recommend you to read again Darwin's account of the horse family and its comparison with pigeons; and if that does not convince and stagger you, then you are unconvertible.

If the situation created by the War has transformed also the English circulation into unconvertible paper money, this is merely a passing fact.

Of the 196 broad-gauge locomotives in service on the Great Western Railway at the end of 1891, sixty-nine were unconvertible to the standard gauge, and were withdrawn from service when Brunel's 7 ft. gauge was finally abolished nearly five months later.