488 PHILOSOPHICAL TRANSACTIONS. [aNNO 1754. 



LXXXI. A Continuation of ihe Account of the JVecither in Madeira. By Dr. 



Thomas Heberden. p. 617. 



This paper contains first a medium of the greatest, least, and mean height of 

 the barometer and thermometer, at Funchal in Madeira, for each month of the 

 years 1751, 1752, 1753, which have but very small differences and changes. 



By collecting the respective sums of the daily heights of the instruments 

 throughout the year, and extracting the mean altitude, it is found that the mean 

 altitude of the barometer for each day, is 29.9 15 inches, and of the thermo- 

 meter, 68°.918. The greatest barometrical variation, during 4 years and 4 

 months, has been -^ of an inch only, viz. from 29.3 to 30.2. The greatest 

 thermometrical variation, during the said time, has been 20", viz. from 60° to 

 80°; but it may be observed, that it never rose so high but once; occasioned by 

 a very strong leste or levant wind ; the extreme height, without such an accident, 

 being never more than 78°. 



The quantity of rain which fell in the 7 years, from 1747 to 1753, inclusive, 

 amounts to 214.346 inches. Therefore the mean quantity for each year is 

 30.62 +. 



LXXXII. On Father Kircher's Opinion concerning the Burning of the Fleet of 

 Marcellus by Archimedes. By James Parsons, M. D., F. R. S. p. 62 1. 



Dr. P. says, that though the machines invented by Archimedes when Mar- 

 cellus besieged the city of Syracuse, as described by Livy, Plutarch, and Poly- 

 bius, were wonders, surpassing the comprehensions of the generality of mankind, 

 yet what was most discredited, was Archimedes's setting fire to the ships, by a 

 burning speculum. Indeed so distinguished a genius, if he could not destroy 

 them in that manner, must know, that he might have thrown combustible matter, 

 sufficient to burn the galleys, from his projectile machines; for we cannot ima- 

 gine that he was ignorant of every kind of these, and not even of the wildfire 

 of the Greeks. But, however, to account for his burning the fleet, by a spe- 

 culum, was the difficult point. 



When philosophers began to increase their catoptrical experiments, which they 

 did very early, they found the focus, of every speculum that was concave, so 

 short, that they were easily inclined to conclude that Archimedes could not set 

 fire to the fleet by a speculum ; and hence the fact became entirely discredited, 

 till Kircher, and his pupil Schottus, whose characters and works the learned 

 world is well acquainted with, resolved to consider not only the story of Archi- 

 medes, but also that of Proclus, who is said to have destroyed a fleet at Con- 

 " stantinople in the same manner. Kircher however, notwithstanding the incre- 

 dulity of the learned of his time, was not deterred from giving attention to the 



