A sudden gust of wind sent a cloud of smoke belching down the shaft. Sanborn shut his eyes and gripped the last staple. He could hear Bill coughing and spluttering down below, while the shaft slowly cleared. Then Sanborn discovered that just above his head the inlet of another chimney joined the main shaft. He decided that the smoke came from there. It must be passed, and quickly, for the air was foul enough without the addition of smoke. Again he tried to wriggle upward, but found that the heat and the fumes from the other shaft were too much for him. He eased down again to the comparative security of the staple. If he could manage to stand on that last staple, he might somehow get past the vomiting side vent. But even if the chimney narrowed above the other shaft, the smoke would be suffocating.