We have already seen that carbon follows quite a different law from the other concrete elements, in the fact that its electrical resistance diminishes as the temperature rises; it also differs widely from the other solid elements in its atomic heat, which has a value much less than one-half the mean constant, which is 6.4. Of this matter of specific heat, Professor Fownes, in his work on chemistry (Bridges' edition), says, "Dulong and Petit observed in the course of their investigation a most remarkable circumstance. If the specific heats of bodies be computed upon equal weights, numbers are obtained all different and exhibiting no simple relations among themselves; but if, instead of equal weights, quantities be taken in the proportion of the atomic weights, an almost perfect coincidence in the numbers will be observed, showing that some exceedingly intimate connection must exist between the relations of bodies to heat and their chemical nature; and when the circumstance is taken into view that relations of even a still closer kind link together chemical and electrical phenomena, it is not too much to expect that ere long some law may be discovered far more general than any with which we are yet acquainted.... Nevertheless, this law must not be understood as perfectly general, for there are three elements--namely, carbon, boron, and silicon" [these form a single group of elements in chemical classification]--"which exhibit decided exceptions to it." Organic chemistry is substantially based upon the almost infinitely interchanging relations among carbon-hydrogen radicals, supplemented by a few other elements. According to Professor Fownes, "Organic chemistry is in fact the chemistry of carbon compounds." The position of carbon among the elements is something like that of camphor among the oils, the latter being a volatile oil, but concrete in form. With a concrete element having the peculiar character of carbon we can well understand its universal chemical and electrical relationship with gaseous hydrogen in the grandest operations of nature.