208 PHILOSOPHICAL TRANSACTIONS. [aNNO 1727- 



little noticed, might serve very well for the same purpose; viz. those vulgarly 

 called shooting or falling stars, being a kind of natural sky-rockets, discharged 

 at a very great height. Now supposing these to be discharged only at 20 or 30 

 miles high, they may be seen by different observers at the same moment of 

 absolute time, in very distant places from each other, which is the thing re- 

 quired : for, if in any two places, as the doctor says, any two observers, by 

 help of pendulum clocks duly corrected by celestial observations, do exactly 

 note at what hour, minute, and second, such a meteor is discharged, the dif- 

 ference of those times will be the difference of longitude of the two places; 

 nor does it require so much as the use of a telescope, as in the methods hitherto 

 practised for that purpose. Now these natural rockets are found to be very 

 frequent in every star-light night ; but especially after a stormy day, or in a 

 stormy night. If therefore persons who are prepared, as above, to be exact in 

 their time, and also have a moderate knowledge of the several constellations, 

 so as to describe the track of any of those meteors among the stars, would but 

 bestow any determinate hour to be agreed among them, as for instance, from 

 8 to 9 each such night, to watch and observe those explosions, noting down 

 immediately the time and track of them, it would be easy to determine, on 

 comparing their observations, which of those explosions each of them see at 

 the same time; and thereby the difference in longitude of those places would 

 be exactly had, as above. 



An Attempt made before the Royal Society, to shoiv how Damps, or foul Air, 

 may be drawn out of all Sorts of Mines, &c. by an Engine contrived by the 

 Rev. J. T. Desaguliers, F. R. S. N° 400, p. 353. 



The engine consists of a triple crank, working 3 pumps, which both suck 

 and force air, by means of 3 regulators, and are alternately applied to drive air 

 into, or draw it from any place assigned, through square wooden trunks ; which 

 being made of slit deal, and 10 inches wide in the inside, are easily portable, 

 and joined to each other without. 



Exper. 1. — Dr. D. filled a tall cylindric glass with the steams of a burning 

 candle and burning brimstone matches, in such manner, that a lighted candle 

 would go out almost as soon as it was let down into that foul air. Then fixing 

 the trunks, or square pipes, to the forcing hole of the engine, he drove fresh 

 air into the bottom of the abovementioned receiver; so that the foul steam 

 came out at the top of the receiver, which was open. 



Exper. 1. — Having filled another receiver, close at top, with foul steams, 

 as before, he placed it in a position almost horizontal, only with the close end 

 something above the open end, that the foul steam might not go out of itself. 



