The pressing of this ball actuates a detonator inside the flask I carry in my pocket.

It's the principle of the pneumatic instantaneous shutter for a camera lens.

The tube leads up--" With a swift disclosing gesture he gave Ossipon a glimpse of an india-rubber tube, resembling a slender brown worm, issuing from the armhole of his waistcoat and plunging into the inner breast pocket of his jacket.

His clothes, of a nondescript brown mixture, were threadbare and marked with stains, dusty in the folds, with ragged button-holes.

"The detonator is partly mechanical, partly chemical," he explained, with casual condescension.
"It is instantaneous, of course ?" murmured Ossipon, with a slight shudder.
"Far from it," confessed the other, with a reluctance which seemed to twist his mouth dolorously.