Jules Theodore Anatole Mallet[1] (23 May 1837 – 10 October 1919) was a Swiss mechanical engineer, who was the inventor of the first successful compound system for a railway steam locomotive, patented in 1874. He is known for having invented three important forms of compound locomotive.
In 1876 he introduced a series of small two-cylinder compound 0-4-2T tank locomotives for the Bayonne-Anglet-Biarritz Railway in France.
He subsequently designed an articulated compound system with a rigid chassis at the rear carrying two high-pressure cylinders, and two low-pressure ones mounted on a swivelling front truck. This was patented in 1884 with full rights granted in 1885.[2] This was first used for a series of narrow gauge locomotives specially built by the Decauville Company in 1888 for the Paris Exposition of 1889.[2] This arrangement became known as the Mallet locomotive. The final developments of these in the USA were some of the largest steam locomotives ever built.
A third compound locomotive, less well-known, was a tandem compound developed in 1890 for SACM as a collaboration with Alfred de Glehn and the Russian A. Borodine. The high and low pressure cylinders were mounted on a common axis, with the high pressure ahead. Unlike the US tandem compounds, the high and low pressure cylinders were cross-connected between sides, which also required them to be receiver compounds with an intermediate reservoir as a pair of curved pipes passing through the smokebox. Large numbers of these, mostly a 2-8-0 derivative, were built for Russian and Hungarian railways making them the most-produced type of tandem compound locomotive. Z. Kordina's design for Hungarian State Railways was a similar 4-4-0, although outside-framed and with the low-pressure cylinders ahead of the high pressure.
He was awarded the Elliott Cresson Medal of The Franklin Institute in 1908.