A Review of the London Volunteer Cavalry and Flying Artillery in Hyde Park in 1804. Unknown artist.
Yale Center for British Art, Paul Mellon Collection.

"The 1804 location is sited above the Titchbourne valley at what is now the Royal Parks HQ in central Hyde Park. The ‘Magazine,’ one of two buildings in the park for storing gun powder would have been nearby."

http://londonaspie.wordpress.com/2013/10/21/the-london-volunteer-cavalry-in-hyde-park-1804/