 Atwater went on to work with Physicist Edward Bennett Rosa and Nutritionist Francis Gano Benedict to design the first direct calorimeter large enough to accommodate human subjects for a period of days.The calorimeter, or human respiration apparatus, was built to precisely measure the energy provided by food.Atwater wanted to use it to study and compare the nutrient contents of different foods and how the human body consumes those nutrients under various conditions of rest and work.