Charles Nicholson, Jr. (1795-1837) was an English flute virtuoso who is remembered for his powerful tone on large-holed flutes of his own design as well as for his expressive powers. He advocated a metalic and reedy tone.

I am playing both flutes with the headjoint pushed all the way in. The pitch, the way I am playing the flutes, is somewhere between A=445 and A=450.

Thomas Prowse Sr. was employed by Clementi & Co. and is believed to have made or supervised the production of their Nicholson's Improved model flutes. See their 1823 catalog offerings. Though not made clear in the catalog, they offered these flutes with various hole sizes. The Clementi used for the musical sample has small (or medium-small) holes. Nicholson advocated flutes with large holes and I do not believe that these small hole models provide the best indication of how Nicholson may have sounded, though judging from surviving flutes, small holed flutes were the most popular. See here for a few photos of a large holed Clementi.

Clementi retired in 1831 and his firm continued as Collard & Collard. Sometime after that, Thomas Prowse Jr. opened a Flute Manufactury and continued to make flutes stamped Ncholson's Improved, almost all of which were large hole models.