Cities
- Until the last few decades, there was no case of a city whose birthrate exceeded its deathrate. In other words, all cities in history, with only a few very recent exceptions, have grown only as a result of immigration (principally from the surrounding countryside).
One of the factors limiting the growth of cities until the last century or so was the difficulty of providing potable water and removing sewage and garbage. Another factor is that the simple proximity of so many people increases the rate at which diseases spread, even with modern public health and sanitation measures, and therefore the rate at which new diseases or new varieties of old diseases appear. That is part of the explanation for the large number of new influenza types discovered in China. It is conceivable that the rise of "civilization" was brought about by a mutation that improved the effectiveness of the human immune system, so that the sustainable size of a city was increased.
Gender-Inclusive Terminology
- Many of the references you will encounter were written before the general recognition of the destructive effects of so-called "inclusive" use of masculine gender in English. Thus, comments about "man" should generally be transposed to "human," and so on.
Even though many of the most well-known scientists and engineers were men, especially prior to 1850, there have been significant contributions by women in all fields of technical endeavor, from the beginning.
Deer, Wolves, and Tribal Peace
- Wolves and people run in packs that occupy fairly specific territories. Deer populations in the wild tend to increase or decrease depending on whether they are located in the center of a predator's territory or in the boundary regions. If the predator (human or wolf) is distracted by the possibility that it might be being stalked, then the deer have a better chance of surviving! If I recall correctly, this point was made in an article in Science in the late 1970s or early 1980s.
Smog in Los Angeles
- Throughout the 1940s, 1950s, and early 1960s the smog in Los Angeles exhibited a smooth exponential growth, corresponding to the population growth and increased use of automobiles. In the early 1960s the state of California passed legislation requiring new automobiles to emit less carbon monoxide. As a consequence, the air quality in Los Angeles was degraded within two years by an amount that would otherwise have taken about twice that long! This was because the true culprit in Los Angeles smog was the emission of oxides of nitrogen, and tuning the engine to produce less carbon monoxide required a hotter flame with more air and less fuel, which in turn increased the formation of oxides of nitrogen. It is routinely (although not always) the case that there will be trade-offs between alternatives, and that legislation that is not adequately informed by detailed technical knowledge can actually make matters worse.
The law was changed to control oxides of nitrogen and other harmful combustion products, as well as carbon monoxide, so that the air quality in Los Angeles did in fact stop deteriorating (the worst year was probably 1968 or 1969), and actually improved even while the population continued to grow. A very nice article on this subject (complete with graph of air quality vs time) appeared in Road & Track in the late 1960s.
Childhood
- The notion of childhood depends on the culture. Industrialized societies of the late 20th century often prolong the transition to full adulthood until well into the 20s. A century or two ago (and in some non-industrialized societies even today), childhood may have ended effectively at an age less than 10. Child Labor Laws are a modern invention, responding in part to industrial society's propensity for labor separated from the family, and in part to their greater wealth that permits removal of older children and younger adults from the labor pool.
Watt's Horsepower
- When Watt commercialized his steam engine, he wanted to be sure that no "four horsepower steam engine" was ever outperformed by any team of four horses. Consequently, the engineering and physics unit of measurement, the "horsepower" (which is a specific amount of energy tranfserred per second), overstates the ability of any horse for sustained work.
Chronometers
- One of the bases for English power in the 1700s and 1800s was sea-borne trade and the naval superiority that protected it. One contribution to that was the ability to determine where on the ocean a ship was located. The angle between the equator and the poles, the latitude, is easy to determine by observing the angle between the horizon and the pole star, or by observing the maximum angle between the sun and the horizon (by definition, this happens at "local noon"). Much more difficult is to determine the longitude, the perpendicular to latitude, nowadays routinely expressed as an angle relative to that of Greenwich, England.
A good book on this subject, written for a general audience, is Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time, by Dava Sobel. Penguin Books, NY, 1995. The key to knowing longitude was the invention of a portable clock that was so accurate that it could provide a worthwhile comparison between local noon and noon at the port of departure, even after a sea voyage of some months.
"Manufacturing" Coal
- What all happens to coal between the ground and the consumer? It must be:
- found;
- broken into small enough pieces;
- removed from the mine;
- separated from adjacent rocks that it may be mixed with;
- sorted by grade (mechanical hardness, chemical heat content...);
- further crushed and possibly sorted by chunk size;
- transported (sometimes powdered and mixed with water to form a "slurry" that can be pumped through pipelines).
Of these, the first three seem to fall into the category of "extraction" or "mining," while the last four might be called "manufacturing" but are perhaps more accurately called "processing."