with one another. Amongst other feats, the boring process involved the first large-scale use of dynamite, a relatively recent innovation that had only been patented in 1867. Another key innovation was the use of mechanised tunneling machines, which the Swiss engineer Louis Favre, supervisor of the work as well as prime contractor, strongly advocated for despite some pressure to make greater use of manual boring. The engineering used to created the tunnel can be largely credited to Favre, although he was unable to see its completion, having suffered a fatal heart attack while inside the tunnel on 19 July 1879, barely six months before breakthrough would be achieved. The tunnel's construction proved difficult on account of multiple factors technical, geological, and financial. The copious supply of water, which was necessary in order to power any heavy equipment at the time, was unreliable; the Tremola spring was one source, but would greatly change in capacity seasonally, leading to water being extracted from the more distant river Ticino instead. At the suggestion of the Geneva-based engineer M. Colladon, it was decided to use compressed air as a means of conveying energy around the worksite and along the bores. Air was compressed by water-driven pumps and stored in cooled reservoirs prior to use; as the air pipes traversed greater and greater distances, the diameter of the pipes used was increased in order to maintain pressure. To reduce the heat of the rock during drilling, water jets were routinely used to cool the rockface. While the geology encounter typically comprised rocks of sufficient hardness for mechanical drilling to be used, those of exceptional hardness were often encountered, resulting in even the best drills being blunted and greatly slowing the rate of advancement, sometimes to as little as one meter per day. There was also a section of entirely disaggregated bedrock encounter, which could only be cleared using traditional manual techniques, which came with the risk of potential collapse. To attain sufficient clearance for the running of trains, the ceiling was vaulted following the completion of advanced boring. The conditions present in either of the bores were thoroughly inhospitable during the tunnel's construction, particularly in the bore driven from Airolo, where vapours were persistently present throughout the work. They were also hazardous; in one major accident alone, around 200 workers (the exact number is not known) were killed largely by the compressed air-driven trains that