1840
	Martin Barry expressed the belief that the spermatozoon enters the egg.	1840
		1841	William Henry Harrison becomes ninth president of the United States; dies one month after inauguration. John Tyler becomes tenth president of the United States.
		1842
	John Stuart Mill publishes Logic.	1843	Congress grants S. F. B. Morse $30,000 to build the first telegraph line (Washington to Baltimore). Sequoyah, Cherokee Indian leader, creates Cherokee syllabary and develops the first written form of a native North American language.
	Darwin first outlines his thoughts on natural selection in an unpublished essay.     Chambers publishes (anonymously) his Vestiges of the Natural History of Creation.	1844
		1845	James K. Polk becomes eleventh president of the United States.
		1846
		1847
		1848
		1849	Zachary Taylor becomes twelfth president of the United States.
		1850