She tried to understand what her father was saying sufficiently to put in a word now and then, but her sense of hearing was strained to its utmost for other sounds.

There was no traffic in the road below, and the house itself was hushed; the ticking of the old clock, performed with such painful effort that it ever seemed on the point of failing, was the only sign of life outside the garret.

At length Emily's ear caught a remote rushing sound; her father's low voice did not overcome it.
'These compounds of nitrogen and oxygen,' he was saying, 'are very interesting.

Nitrous oxide, you know, is what they call Laughing Gas.
You heat solid nitrate of ammonia, and that makes protoxide of nitrogen and water.' The words conveyed no sense to her, though she heard them.

The rushing sound had become a dull continuous thunder.