| 摘要 |
The trap comprises an elongated pipe 1 whose first open end 3 is intended to be pushed into a tunnel, the second end 4 being closed by a detachable lid 5 having a central hole 7 to allow light to enter, while a nonreturn shutter 10 is arranged inside the tube and provided with a hole 12 which is aligned with the former to allow the passage of light. <IMAGE>
|
