By the “London Mechanics' Magazine” of March 26th, we learn that a number more of trials have been made with Marston's Ameri- can Rifle in London, all of which have given great satisfaction. It is about to come into extensive use in the French and British iar-mies. The rapidity with which it can be loaded and discharged, and the self-cleaning operation of each cartridge make it the prince offire-arms.