In 1748 Franklin, being then forty-two years old, and in the enjoyment of an ample income from his business as printer and publisher, sold out to his foreman, David Hall, and was free to devote himself wholly to his beloved experiments. He had built himself a home in a retired spot on the outskirts of Philadelphia, and with an income which in our days would be equivalent to $15,000 or $20,000 a year, he was considered a fairly rich man. Having thus settled his business affairs in a manner which proved that he knew perfectly well what money was worth, he took up his electrical studies again and extended them from the machine to the part played in nature by electricity. The patience with which he observed the electrical phenomena of the heavens, the acuteness displayed by him in drawing plausible inferences from his observations, and the rapidity with which he arrived at all that we now know of thunder and lightning, still excite the astonishment of all who read the narratives he has left us of his proceedings. During the whole winter of 1748-49 and the summer following, he was feeling his way to his final conclusions on the subject. Early in 1749 he drew up a series of fifty-six observations, entitled "Observations and Suppositions towards forming a new Hypothesis for explaining the several Phenomena of Thundergusts." Nearly all that he afterward demonstrated on this subject is anticipated in this truly remarkable paper, which was soon followed by the most famous of all his electrical writings, that entitled "Opinions and Conjectures concerning the Properties and Effects of the Electrical Matter, and the Means of preserving Buildings, Ships, etc., from Lightning; arising from Experiments and Observations made at Philadelphia, 1749." Franklin sets forth in this masterly paper the similarity of electricity and lightning, and the property of points to draw off electricity. It is this treatise which contains the two suggestions that gave to the name of Franklin its first celebrity. Both suggestions are contained in one brief passage, which follows the description of a splendid experiment, in which a miniature lightning-rod had conducted harmlessly away the electricity of an artificial thunder-storm. "If these things are so," continues the philosopher, after stating the results of his experiment, "may not the knowledge of this power of points be of use to mankind in preserving houses, churches, ships, etc., from the stroke of lightning, by directing us to fix on the highest part of those edifices upright rods of iron, made sharp as a needle and gilt to prevent rusting, and from the foot of those rods, a wire down the outside of the building into the ground, or down round one of the shrouds of a ship, and down her side till it reaches the water? Would not these pointed rods probably draw the electrical fire silently out of a cloud before it came nigh enough to strike, and thereby secure us from that most sudden and terrible mischief?"