The story is also notable in that Verne attempted to do some rough calculations as to the requirements for the cannon and, considering the total lack of any data on the subject at the time, some of his figures are surprisingly close to reality. Most interestingly, his estimate of the cost of the project in 1865 dollars is near the cost of the Apollo 11 flight in 1969 dollars.
Due to its age, the text is now out of copyright and can be downloaded from Project Gutenberg from http://www.ibiblio.org/gutenberg/cgi-bin/sdb/t9.cgi?entry=83&full=yes&ftpsite=http://www.ibiblio.org/gutenberg/