The above writer considers, and with reason, that when the uncertainty of firearms was taken into consideration defensive armour was of much practical use; and this theory was held as late as the eighteenth century, for Marshal Saxe in his _Les Rêveries_[82] warmly recommends the use of defensive armour, especially for cavalry, as he considers that a large proportion of wounds were caused by sword, lance, or spent bullets. It was evidently from reasons such as the above that a reliable proof by pistol or musket shot was insisted upon, for the armour of the Duc de Guise in the Musée d’Artillerie (G, 80) is of great thickness and weighs 42 kilos. It has either been tested by the maker or has seen service, for there are three bullet marks on the breastplate, neither of which has penetrated.[83] 1569. _Arch. cur. de Nantes_, I, col. 305. 612 corps de cuyrace ... garnis de haulzecou ... desquelz le devant sera a l’espreuve d’arquebuse et le derrière de pistol. The terms “high proof,” “caliver proof,” and “musket proof” often occur in writings of this period and onwards up to the time when armour was discarded; but it is difficult to get any definite information as to how the proof was made. In the above entry there are two kinds of proof, which show that the back-plate was thinner than the breastplate, the resisting power being obtained not only by temper of metal, but also by its thickness. 1568. _Les Armuriers français et étrangers_, Giraud, pp. 191, 192. Ung corps de cuirasse lequel sera a l’espreuve de la pistolle, ung habillement de teste a l’esprouve de la pistolle, brassartz ... a l’esprove de la pistolle, tassettes courtes a l’esprouve de la pistolle. Here is evidently a necessary definition of each piece. Probably on some former occasion the armourer had classed the whole suit as of proof when such a description might only be honestly given to the cuirass. Accounts of actual trials are rare, but the following extract is of interest as showing the methods employed in England. It is given in full, with many valuable extracts bearing on the craft of the armourer, by Viscount Dillon, in _Archæologia_, Vol. LI. The extract is taken from a letter from Sir Henry Lee, Master of the Armoury in 1580, to Lord Burghley, and bears the date Oct. 12, 1590.