century saw a tremendous amount of technological progress, which inspired authors to write in the genre of science fiction. H. G. Wells' The Time Machine (1895) was a commercial success; in it, he introduced the notion of time travel. In some instances, science fiction inspired new technology and scientific research. Explorer Ernest Shackleton acknowledged that the novel Twenty Thousand Leagues Under the Sea by Jules Verne was an inspiration. As reading became more pronounced in the 19th century with public notes, broadsides, catchpennies and printed songs becoming common street literature, it informed and entertained the public before newspapers became readily available in the later 19th century. Advertisements and local news, such as offers of rewards for catching criminals or for the return of stolen goods, appeared on public notices and handbills, while cheaply printed sheets – broadsheets and ballads – covered political or criminal news such murders, trials, executions, disasters and rescues. Chapbooks would also be common place, these were simple reading matter that were small, cheap forms of literature for children and adults that were sold on the streets, their subjects included fiction writing to disaster updates. Their readership would have been largely among the poor, and among children of the middle class. A 2015 study investigated the frequency at which difficult vocabulary from the WORDSUM test were employed in about 5.9 million English-language texts published between 1850 and 2005. The researchers found that the more difficult of words were in declining usage and that there was a negative correlation between the use of such words and completed fertility. On the other hand, simpler words entered increasingly common use, an effect of rising literacy. In another study, from 2017, researchers employed Google's Ngram Viewer, an enormous archive of scanned books, periodicals, and other printed materials dating back to the sixteenth century. They found that the use of difficult vocabulary increased substantially between the mid-1700s and mid-1800s before declining steadily till the present day. Entertainment Popular forms of entertainment varied by social class. Victorian Britain, like the periods before it, was interested in literature, theatre and the arts (see Aesthetic movement and Pre-Raphaelite Brotherhood), and music, drama, and opera were widely attended. Michael Balfe was the most popular British grand opera composer of the period, while the most popular musical theatre was a series of fourteen comic operas by Gilbert and Sullivan, although there was also musical burlesque and the