fruit and wheat by the time Grey left in 1845, contrasting with a low point in 1842 when one-third of Adelaide houses were abandoned. Trade links with the rest of the Australian states were established after the Murray River was successfully navigated in 1853 by Francis Cadell, an Adelaide resident. South Australia became a self-governing colony in 1856 with the ratification of a new constitution by the British parliament. Secret ballots were introduced, and a bicameral parliament was elected on 9 March 1857, by which time 109,917 people lived in the province. In 1860, the Thorndon Park reservoir was opened, providing an alternative water source to the now turbid River Torrens. Gas street lighting was implemented in 1867, the University of Adelaide was founded in 1874, the South Australian Art Gallery opened in 1881 and the Happy Valley Reservoir opened in 1896. In the 1890s Australia was affected by a severe economic depression, ending a hectic era of land booms and tumultuous expansionism. Financial institutions in Melbourne and banks in Sydney closed. The national fertility rate fell and immigration was reduced to a trickle. The value of South Australia's exports nearly halved. Drought and poor harvests from 1884 compounded the problems, with some families leaving for Western Australia. Adelaide was not as badly hit as the larger gold-rush cities of Sydney and Melbourne, and silver and lead discoveries at Broken Hill provided some relief. Only one year of deficit was recorded, but the price paid was retrenchments and lean public spending. Wine and copper were the only industries not to suffer a downturn. 20th century Adelaide was Australia's third largest city for most of the 20th century. Electric street lighting was introduced in 1900 and electric trams were transporting passengers in 1909. 28,000 men were sent to fight in World War I. Historian F. W. Crowley examined the reports of visitors in the early 20th century, noting that "many visitors to Adelaide admired the foresighted planning of its founders", as well as pondering the riches of the young city. Adelaide enjoyed a postwar boom, entering a time of relative prosperity. Its population grew, and it became the third most populous metropolitan area in the country, after Sydney and Melbourne. Its prosperity was short-lived, with the return of droughts and the Great Depression of the 1930s. It later returned to fortune under strong government leadership. Secondary industries helped reduce the state's