Since de Langen published his results only in Dutch , his work remained unknown to most of the international scientific community .
De Langen 's colleague , Isidor Snapper , made a similar observation in North China in 1940 .
Since de Langen published De Langen 's results only in Dutch , De Langen 's work remained unknown to most of the international scientific community .
De Langen 's colleague , Isidor Snapper , made a similar observation in North China in 1940 .