In later years proof took place at other government grounds, all within the London area. In Moorfields, according to Stowe, was the Artillery Yard, “whereunto the gunners of the Tower do weekly repair; and there, levelling certain brass pieces of great artillery against a butt of earth made for that purpose, they discharge them for their exercise.”[58] Spitalfields also had its artillery butts. “Where Liverpool-street Station now stands the Tower gunners of Elizabeth’s day had their yard, and there discharged great pieces of artillery for exercise, while throughout the seventeenth century guns were both cast and tested in the vicinity, as Gun-street, Fort-street, and Artillery Lane hard by serve to remind us. Finsbury Field, levelled for an archery ground in 1498, passed from the London archers to the London gunners, and, as the Honourable Artillery Company’s Ground, survives to carry on the long traditions of the spot.”[59] Under the Commonwealth progress was made in the quality of gunpowder, and improved methods were introduced of testing it for strength and uniformity. This advance had its effect on the guns. Failures were frequent, and, in spite of improved founding, pieces had to be made heavier than before; cast iron in particular was found unequal to withstanding the stresses caused by the improved powders, and this metal came into such disfavour that a whole century elapsed before it was again accepted as suitable by both naval and military artillerists. Founding in bronze had undergone improvement. Malthus, an Englishman who had risen in the French service to be Director of their Artillery,[60] mentions in his _Pratique de la Guerre_, as evidence of this improvement, the fact that in breaking up old pieces lumps of free tin and copper were frequently discovered, whereas in the case of new guns the metal was invariably found well-mixed.