Source Data Reference for:

City = Dusseldorf
Time = 1850

City	Year	Size	Size Comment	Year Comment	Author	Title	Location
Dusseldorf	1850	33,000			Tertius Chandler	Four thousand years of urban growth	p26
Dusseldorf	1850	41,000			Paul Bairoch	La population des villes europeennes de 800 a 1850
Dusseldorf	1861	37,900		1861/62	n/a	Gothaischer Hofkalender