（解説文要約）
この作品には、捲き上げられた炭車が選炭場まで運ばれる様子が描かれています。
坑口が撰炭機の近くにあって場所が狭い場合、

引き揚げた炭車から捲き上げ機のロープをはずし、自走させて選炭場まで移動させていました。
誤って炭車を坑内へ逆走させると大変な事故になります。そこで、逆走を防ぐ安全器が必要でした。

 

 

 

 

This painting describes how coal cars were transferred to the coal dressing site after being winched out from the pit.
When the dressing machine was located near the pit entrance in a narrow space, the cars were released from the winch rope and would then run down to the dressing site by self-propulsion.
But if the car was mistakenly released in the opposite direction, running down into the pit again, it could lead to a serious accident.
Therefore, a safety device to prevent the cars from releasing backwards was essential and invented.