and their causes.  He maintains that influenzas usually classed as colds do not arise, as a rule, from either cold or dampness.  He points out that savages and sailors, who are often wet, do not catch cold, and that the disease called a cold is not taken by swimming.  He maintains that people who live in the forest, in open barns, or with open windows, do not catch cold, and that the disease called a cold is generally caused by impure air, lack of exercise, or overeating.  He comes to the conclusion that influenzas and colds are contagious—­a doctrine which, a century and a half later, was proved, through the advance of bacteriological science, to be sound.  The following sentence exhibits remarkable insight, considering the state of medical art at that time:  “I have long been satisfied from observation, that besides the general colds now termed influenzas (which may possibly spread by contagion, as well as by a particular quality of the air), people often catch cold from one another when shut up together in close rooms and coaches, and when sitting near and conversing so as to breathe in each other’s transpiration; the disorder being in a certain state.”  In the light of present knowledge what a cautious and exact statement is that!

There being no learned society in all America at the time, Franklin’s scientific experiments were almost all recorded in letters written to interested friends; and he was never in any haste to write these letters.  He never took a patent on any of his inventions, and made no effort either to get a profit from them, or to establish any sort of intellectual proprietorship in his experiments and speculations.  One of his English correspondents, Mr. Collinson, published in 1751 a number of Franklin’s letters to him in a pamphlet called “New Experiments and Observations in Electricity made at Philadelphia in America.”  This pamphlet was translated into several European languages, and established over the continent—­particularly in France—­Franklin’s reputation as a natural philosopher.  A great variety of phenomena engaged his attention, such as phosphorescence in sea water, the cause of the saltness of the sea, the form and the temperatures of the Gulf Stream, the effect of oil in stilling waves, and the cause of smoky chimneys.  Franklin also reflected and wrote on many topics which are now classified under the head of political economy,—­such as paper currency, national wealth, free trade, the slave trade, the effects of luxury and idleness, and the misery and destruction caused by war.  Not even his caustic wit could adequately convey in words his contempt and abhorrence for war as a mode of settling questions arising between nations.  He condensed his opinions on that subject into the epigram:  “There never was a good war or a bad peace.”