Latimer started working at Crosby and Gould, a patent law firm. He learned to draw diagrams. While at the law firm, Latimer invented an improved railroad car bathroom and an early air conditioning unit. Later, Latimer helped Alexander Graham Bell by drawing diagrams for his patent for the first telephone. Latimer also helped Thomas Edison with his patent for the light bulb, and invented a better way to make carbon filaments for light bulbs.