He stood still, staring after the two, and saw Marietta tap upon the door of the glass-house.

It opened almost immediately and they disappeared within.
As soon as they were out of sight, his anger broke out, and he made a few quick steps on the bridge.

Then he stopped, for he was afraid to make a scandal.

That at least was what he said to himself, but the fact was that he was afraid to face his sister, who was infinitely braver and cooler than he.

Besides, he reflected that he could not now prevent her from going to the laboratory, since she was already there, and that it would be very undignified to make a scene before Zorzi, who was only a servant after all.