While such ideas prevailed among the majority of men, the rational study of science could make little progress. In the march of the ages as the ideas of men were classified, it began to be understood that the claims of the devotees of the mystical arts not only could not be substantiated but were in direct opposition to the known operations of nature. It became clear to the truthseekers, that in nature a given cause, acting upon any given object, providing all surrounding conditions be left unchanged, will always produce the same effect. Thus, coal of a certain quality, brought to a high temperature in the presence of air, will burn and produce heat; a stick held in water at the right angle will appear crooked; iron kept in contact with moisture and air, at the right temperature, will be changed into rust; sunlight passed through a glass prism will be broken into rainbow colors; ordinary plants placed in a dark cellar will languish and die. No matter how often trials are made, the above results are obtained; and today it is safe to assert that in the material world no relation of cause and effect, once established, has failed to reappear at the will of the investigator. As this principle of the constancy in the relations between cause and effect was established, the element of chance in natural phenomena, with its attendant arts of magic, had to disappear. It is now well understood by intelligent persons that the law of order controls all the elements of nature. It is true that the cause of any given effect may, itself, be the effect of other causes, and that the first cause of daily phenomena is not and probably cannot be understood. It is also true that very seldom is the mind able to comprehend why certain causes, save the simpler ones, should produce certain effects. In that respect we are again nothing more than Plato's cave prisoners, seeing the shadows of ultimate realities. However, the recognition of the principle of the invariable relation between cause and effect was a great onward stride in the intellectual development of the world. [Sidenote: Laws of nature are man's simplest expression of many related facts.] Now, as men began to investigate nature with her forces, according to the new light, numerous relations of the forces were discovered--in number far beyond the comprehension of the human mind. Then it was found necessary to group all facts of a similar nature, and invent, if possible, some means by which the properties of the whole group might be stated in language so simple as to reach the understanding. Thus came the laws of nature.