MEMOIR OF THE LATE DR. HENRY. 137 
of Dr. Henry’s contributions to chemical know- 
ledge, it must be borne in mind that in his sea- 
son of greatest mental activity, he never en] oyed 
that uncontrolled command of time, and that 
serene concentration of thought, which are 
essential to the completion of great scientific 
designs. His intellectual seedtime was en- 
croached upon by the duties of an extensive 
medical practice, and by other equally pressing 
avocations, and his experimental enquiries were 
conducted at late hours or at intervals snatched 
from engrossing pursuits and with the liability 
to constant interruptions. In more advanced 
life, when relieved from. such exertions, growing 
infirmities and failing bodily power restrained 
him to studies not demanding personal exertion, 
and even abridged his season of purely mental 
labour. That amid circumstances so unfriendly 
to original and sustained achievements in 
science, he should have accomplished so much, 
bears testimony to that energy of resolve, that 
unsubdued ardour of spirit, which ever glowed 
within him, urging him steadily onwards in the 
career of honourable ambition, and prompting 
exertions more than commensurate with the 
decaying forces of a frame that had never been 
vigorous. 
