Alexander Henderson contributed to which compendium, written by about 100 full-time editors and 4,000 contributors at current?
Alexander Henderson (physician):  He chiefly devoted himself to letters, though, contributing to such works as "Encyclopædia Britannica" and "Edinburgh Review". Encyclopædia Britannica:  It is written by about 100 full-time editors and more than 4,000 contributors, who have included 110 Nobel Prize winners and five American presidents.
Encyclopædia Britannica