VOL. XLVII.] PHILOSOPHICAL TRANSACTIONS. 



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LXXXVII. A farther Account of the late Plague at Constantinople, in a Letter 

 from Dr. Mackenzie, of the 23d of April, 1752. p. 514. 

 As a corollary to his former account sent to Dr. Mead, Dr Mackenzie sub- 

 joins that, on January 3, 1732, there was an accident of the plague, when the 

 thermometer was at 53. Jan. 24, another accident, therm. 62. Jan. 26, an 

 accident at Buiukdere, therm. 51. Feb. 8, accidents at Cassim, Pacha, and 

 Phanar, therm. 52. Feb. 10, an accident in Galata, therm. 55; patient re- 

 covered. Feb. 15, another accident in the same house, therm. 53. March 8, 

 an accident in Galata, therm. 56 ; and not one accident afterwards, though at 

 the above date the thermometer was at 50, and had been at 44 the l6th instant ; 

 so that they had great hopes to get clear, if no infection should be conveyed to 

 them from any other quarter. 



Prosper Alpinus observes, that the etesian winds at Cairo remove the plague 

 entirely ; so that they fear nothing after these winds begin. And Dr. M. was 

 assured that all the plagues which had been at Smyrna and Constantinople for 

 the last 20 years, had been most violent during the season of the etesian winds; 

 still allowing that were it not for the etesian winds, the plague would be more 

 violent in the hot months. 



LXXXFIII. A Letter of Mr. James Short, F. R. S. to the Royal Society, con- 

 cerning the Inventor of the Contrivance in the Pendulum of a Clock, to pre- 

 vent the Irregularities of its Motion by Heat and Cold. p. 517. 

 Soon after the invention of pendulum-clocks, justly ascribed to the celebrated 

 Huygens, it was found that they were liable to considerable inequalities in their 

 motion ; which were imagined to rise from the pendulum, in its vibrations, de- 

 scribing an arc of a circle , and consequently that the larger vibrations must be 

 slower than the shorter ones. In order to remedy this imperfection, Mr. 

 Huygens wrote a treatise, called Horologium oscillatorium, a piece of geometry 

 which does honour to the last century, in which he demonstrates, from the pro- 

 perties of the cycloid, that the vibrations of a pendulum, moving in a cycloid, 

 would be performed in equal times, even though the vibrations were unequal. 

 Pendulums therefore were made to vibrate in a cycloid ; but great inequalities 

 were still observed in the motion of clocks. 



We do not read of any attempts after this, to regulate the motion of clocks 

 till the year 1720, when Mr. George Graham delivered into the Royal Society a 

 paper, which is published in the Phil. Trans. N" 392, in which he says, that it 

 having been apprehended, that the inequalities in the motion of clocks arose from 

 a change of length in the pendulum, by the influences of heat and cold, he, 

 about the year 1715, made several trials, in order to discover, whether there 



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