EVOLUTION OF THE THERMOMETER
I. The Open Air-Thermometer of Galileo.
Discoveries and inventions are sometimes the product of the genius or of the intelligent industry of a single person and leave his hand in a perfect state, as was the case with the barometer invented by Torricelli, but more often the seed of the invention is planted by one, cultivated by others, and the fruit is gathered only after slow growth by some one who ignores the original sower. In studying the origin and tracing the history of certain discoveries of scientific and practical value one is often perplexed by encountering several claimants for priority, this is partly due to the circumstance that "coincidence of independent thought is often the cause of two or more persons reaching the same result" about the same time; and partly to the effort of each nation to secure for its own people credit and renown. Again, the origin of a prime invention is some-
