Xll MEMOIR OF BUFFON. 



cing the plan, it was necessary to perform many preliminary experi- 

 ments, relating to the loss of light by reflection, and the best materials 

 which could be used for the construction of the lenses. These accom- 

 plished, he commenced to build his great mirror. It was composed of 

 168 pieces of plain silvered glass, six inches by eight in size, and he 

 required to examine above 500 pieces before the most perfect could 

 be obtained. Between each was an interval of four lines, to allow a 

 free motion, and to permit the observer to see the place, to which the 

 images were to be thrown. The whole were mounted in an iron frame 

 so fitted with screws and springs, that a motion could be given to 

 them in any direction, and the images reflected from all the mirrors 

 easily thrown upon the same spot. In eight experiments, he obtained 

 the following results, which clearly show the possibility of setting fire 

 to the Roman fleet : — On March 23d, a plank of tarred beech was set 

 on fire at sixty-six feet, with only forty mirrors, and without the 

 mirror being put upon its stand. On the same day, a plank tarred 

 and sulphured, and having the mirror more disadvantageously placed, 

 was fired, at the distance of 126 feet, with 98 mirrors. On the 3d of 

 April, at four o'clock in the evening, a slight inflammation was made 

 upon a plank covered with wool cut into small pieces, distant 138 feet, 

 with 112 mirrors. The next day, at eleven o'clock forenoon, 1.54 

 mirrors, at the distance of 150 feet, made a tarred plank smoke to 

 such a degree in two minutes, that it would have been inflamed had 

 not the sun disappeared. On the 5th April, a dull day, at three o'clock 

 in the afternoon, 154 mirrors, at a distance of 250 feet, inflamed in 

 two minutes and a half, minute chips of deal, sulphured and mixed 

 with charcoal. When the sun was vivid, the inflammation took place 

 in a few seconds. On the 10th April, after mid-day, with a clear sun, 

 128 mirrors, at the distance of 150 feet, set fire to a tarred plank of 

 fir; the inflammation being very sudden. Same day, at half-past two, 

 148 mirrors, at 150 feet, fired a plank of beech sulphured in some 

 parts, and in others covered with wool cut into small pieces ; the inflam- 

 mation was so sudden and violent, that it was necessary to plunge the 

 plank into water in order to extinguish it. April 1 1 , twelve mirrors, 

 at twenty feet, inflamed some combustible matters ; forty-five, at 

 twenty feet, melted a large pewter flask that weighed six pounds ; 

 and 117 made some thin pieces of silver and iron red-hot. Having 

 satisfied himself upon this point, he followed out the subject, and con- 

 structed mirrors upon various plans. Perhaps the most remarkable 

 were those formed by bending glass upon moulds of a spherical form 

 by means of a furrow ; he was thus able to make them of very consi- 

 derable size, but they required great caution in the cooling and grinding 



