Page:Works of the Late Doctor Benjamin Franklin (1793).djvu/143

133 diſtance, commenced at Philadelphia nearly four hours before it was felt at Boſton. He endeavoured to account for this, by ſuppoſing that, from heat, ſome rarefaction takes place about the gulph of Mexico, that the air further north being cooler ruſhes in, and is ſucceeded by the cooler and denſer air ſtill further north, and that thus a continued current is at length produced.

The tone produced by rubbing the brim of a drinking glaſs with a wet finger had been generally known. A Mr. Pockrich, an Iriſhman, by placing on a table a number of glaſſes of different ſizes, and tuning them by partly filling them with water, endeavoured to form an inſtrument capable of playing tunes. He was prevented by an untimely end, from bringing his invention to any degree of perfection. After his death ſome improvements were made upon his plan. The ſweetneſs of the tones induced Dr. Franklin to make a variety of experiments; and he at length formed that elegant inſtrument, which he has called the Armonica.

In the ſummer of 1762 he returned to America. On his paſſage he obſerved the ſingular effect produced by the agitation of a veſſel, containing oil floating on water. The ſurface of the oil remains ſmooth and undiſturbed, whilſt the water is agitated with the utmoſt commotion. No ſatisfactory explanation of this appearance has, we believe, ever been given.

Dr. Franklin received the thanks of the aſſembly of Pennſylvania, "as well for the faithful diſcharge of his duty to that province in particular, as for the many and important ſervices done to America in general, during his reſidence in Great Britain." A compenſation of 5000l. Pennſylvania currency was alſo decreed him for his ſervices during ſix years.