de Prony brake dynamometers at a tractor contest in 1910. Schematic of a de Prony brake. The de Prony Brake is a simple device invented by Gaspard de Prony to measure the torque produced by an engine. The term  brake horsepower  is one measurement of power derived from this method of measuring torque. (Power is calculated by multiplying torque by rotational speed .).
Typically tree trunks are thought of as being in various shades of brown. They can have many different colours to them, however.Grey is a common colour in tree trunks, as is green when they're younger. Specific species of trees usually have specific bark colour at specific times of year so you should look up the trees you're interested in if you need more information.ypically tree trunks are thought of as being in various shades of brown. They can have many different colours to them, however.
Some mixtures give rise to the reddish and purplish fall colors of trees such as dogwoods and sumacs, while others give the sugar maple its brilliant orange. The autumn foliage of some trees show only yellow colors. Others, like many oaks, display mostly browns. All these colors are due to the mixing of varying amounts of the chlorophyll residue and other pigments in the leaf during the fall season.