top of each other, separated by a layer of cloth or cardboard soaked in brine (i.e., the electrolyte). Unlike the Leyden jar, the voltaic pile produced continuous electricity and stable current, and lost little charge over time when not in use, though his early models could not produce a voltage strong enough to produce sparks. He experimented with various metals and found that zinc and silver gave the best results. Volta believed the current was the result of two different materials simply touching each other – an obsolete scientific theory known as contact tension – and not the result of chemical reactions. As a consequence, he regarded the corrosion of the zinc plates as an unrelated flaw that could perhaps be fixed by changing the materials somehow. However, no scientist ever succeeded in preventing this corrosion. In fact, it was observed that the corrosion was faster when a higher current was drawn. This suggested that the corrosion was actually integral to the battery's ability to produce a current. This, in part, led to the rejection of Volta's contact tension theory in favor of the electrochemical theory. Volta's illustrations of his Crown of Cups and voltaic pile have extra metal disks, now known to be unnecessary, on both the top and bottom. The figure associated with this section, of the zinc-copper voltaic pile, has the modern design, an indication that "contact tension" is not the source of electromotive force for the voltaic pile. Volta's original pile models had some technical flaws, one of them involving the electrolyte leaking and causing short-circuits due to the weight of the discs compressing the brine-soaked cloth. A Scotsman named William Cruickshank solved this problem by laying the elements in a box instead of piling them in a stack. This was known as the trough battery. Volta himself invented a variant that consisted of a chain of cups filled with a salt solution, linked together by metallic arcs dipped into the liquid. This was known as the Crown of Cups. These arcs were made of two different metals (e.g., zinc and copper) soldered together. This model also proved to be more efficient than his original piles, though it did not prove as popular. Another problem with Volta's batteries was short battery life (an hour's worth at best), which was caused by two phenomena. The first was that the current produced electrolyzed the electrolyte solution, resulting in