Once the mind was cleared of its idols, it would be able to discover causes through experimentation. Francis Bacon (1561–1626) thought that all of nature was made up of bodies or material objects that acted according to fixed laws. These laws were the “forms” of material objects. In seeking causes, first we must look for those things from which certain other things always follow. (For example, heat is followed by a motion of particles.) Next, we look for the cases where the effects do not happen when the cause is absent. (No heat, no movement of particles.) When what we are studying occurs to a greater or lesser degree, we must be able to account for the variation. Whenever possible, we should invent instruments to measure what we are investigating. (In this case, thermometers and barometers.)