1. Conservation of Energy

The middle of the nineteenth century witnessed the discovery of all three of the great unifications of science. These are the unification of energy by the discovery of the principle of the conservation of energy, the unification of matter by the discovery of the periodic system, and the unification of life by the work of Charles Darwin.

Not for decades after Bolton and Watt, as the result of commercial necessity, introduced the idea of measuring energy in horsepower, was the real nature of the relationship between heat and mechanical power critically examined, save once in a quickly forgotten investigation by Sadi Carnot. But at length the speculations and calculations of Julius Robert Mayer, the admirable experimental researches of Joule, and the profound studies of Helmholtz and others established the principle of the conservation of energy〖H. C., XXX, 173ff.〗—in short, demonstrated the proposition that energy is one and indestructible, however it may manifest itself as heat, or light, or electricity, or otherwise.

2. Periodicity

Somewhat later the work of Newlands, Lother Meyer, and Mendeléeff brought to light an extraordinary series of relationships, periodically recurring properties, among the elements. It would be impossible briefly to explain this relationship, but a simple analogy may serve to show its nature.

11     12     13     14     15

21     22     23     24     25

31              33     34     35

41     42     43              45

51     52     53     54     55

Giving the numbers above arranged, there can be no doubt, first, that they have been correctly arranged, and secondly, that the numbers 32 and 44 are missing, but have a place in the table. In other words, it is possible to predict the “properties” of the two missing numbers. In like manner, the studies of Mendeléeff showed similar connections among the elements. These could be arranged, as he showed, in the order of their atomic weights, in a table very similar to the above, in which the variation in properties was regular and periodically recurrent, but with certain gaps in the classification. Judging from the elements surrounding such gaps, Mendeléeff predicted the properties of the missing elements in certain cases in which the missing elements have now been supplied by chemical research. The results have invariably confirmed the Russian chemist’s predictions, as may be seen from the following data concerning the element germanium: 

                                                            PREDICTION               OBSERVATION

Atomic weight                                            72.0                               72.3

Specific gravity                                          5.5                                 5.469

Atomic volume                                           13.0                              13.2

Specific gravity of oxide                            4.7                                4.703

Boiling point of chlorideLess than            100°                            86°

Specific gravity of chloride                        1.9                               1.9

Specific gravity of ethyl compound 0.96 Lower than water

Thus it has become clear that the elements are all related to one another. It is not known how to explain this relationship—perhaps they have been evolved in an orderly manner from something else—but, at all events, matter is not only indestructible (Lavoisier), but it makes up a unitary system. To-day we feel sure that we are acquainted with nearly all the stable varieties of matter that exist in the universe, though of course there remain a great variety of arrangements of this matter which are unknown to us.

3. Biological Evolution

The only well-known phenomenon that cannot be completely described in terms of matter and energy is life, with its peculiar characteristics of consciousness and thought. In the year 1859 biology yielded to the unifying idea of Charles Darwin. Many had previously suspected that all living things are blood relations; the discoveries of embryologists in particular had proved that the similarities among living things are far more profound than had been formerly realized. But Darwin provided a plausible explanation of the development of more complex beings by a continuous evolutionary process, and this led to the world’s final decision in favor of the hypothesis of transformation.

It is possible that some of Darwin’s hypotheses may in the end be discarded, but it appears to be wholly unlikely that the world will ever give up its belief in the evolution of organic beings, in all their multitudinous forms, from earlier and simpler types, and probably originally from one or more exceedingly simple forms.

Finally, the change in the relation of science to civilization, accomplished in the nineteenth century, marks a new epoch in history. For the first time humanity has systematically undertaken the task of conquering the environment. A new organ of the social body, like the financial or the military, has been created and has assumed relations with the other parts of the great organism of modern society.

System replaces chance in the greater part of human affairs, manufacturing, warfare, medicine, commerce itself, have become “scientific”; they advance steadily, ruthlessly, and carry man with them; whither he cannot guess.

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