Machine Gun : Dr. Richard Gatling

Malarial Parasite : Ronald Ross

Match (safety) : J.E. Lurdstrom

Mathematical Astro Physics : Chandrasekhar
Mathematical Genius : Carl Gauss (Karl Friedrich Gauss)
Mauve : dye Perkin
Measurement of Electrical Energy Joule : James Prescoft
Mechanical Equivalent of Heat : Joules
Mercury Thermometer : Fahrenheit
Meson Hideki : Yakawa Microphone : Johann Phillip Reis, Alexander Graham Bell, Elisha Gray, Amos E. Dolbear, and Thomas Edison
Microscopic Anatomy : Marcello Malpighi
Modern Anthropology : Franz Boas
Modern Astronomy : Arthur Eddington
Modern Computer : John von Neumann
Modern Geology : Charles Lyell
Modern Physiology : William Bayliss
Modern Synthesis : Theodosius Dobzhansky
Modern Telescope : Edwin Hubble
Molecular Biology : Francis Crick
Molecular Scattering of light in fluid : Ramanathan
Montessori Method : Maria Montessori
Motion of the Planets : Johannes Kepler
Motor Car (petrol) : Karl Butler
Movie Projector : Thomas Alva Edison