Dr. Burney in reply to Mr. Squire. 209 



tober 1823. I observed also that the mercury in Mr. VealPs 

 barometer, and in Mr. Cary's, was pretty regular in its descent 

 from the 9th to the 15th of May, and that it was a day later 

 in arriving at the minimum pressure in that change than in 

 mine. The conclusions I drew on these phenomena at the 

 time, to satisfy myself of the probable accuracy of the JBoston 

 observations, were these : — I first considered the position of 

 the wind here, which had blown very strong from the N.E. 

 from the 9th to the 14th ; also the latitude of Boston, which 

 is upwards of two degrees north of Gosport, and thought that 

 the difference of 3jr inches depth of rain between Gosport and 

 Boston, from the 9th to the 15th of May, would account sa- 

 tisfactorily for the greater altitude of the mercury in Mr.VeaH's 

 barometer, viz. -j% of an inch more than its mean altitude in 

 comparison of mine. If the wind, which accompanied this 

 unprecedented fall of rain here, had blown from the north or 

 west, the difference in the quantity of rain and the state of the 

 barometer at Boston, would undoubtedly have been very dif- 

 ferent. Considering the position of the wind N.E., and the 

 latitude of Boston, it is very probable that the rain-cloud was 

 so much attenuated over the latter place, as to afford but little 

 rain ; for it sometimes happens in travelling that we see very 

 awful thunder storms at a distance of 10 or 12 miles, ivhile we 

 enjoy a dry air with scarcely a cloud. 



I believe it can be easily proved by calculation that the pre- 

 cipitation of 3 j inches depth of rain from the atmosphere, is 

 nearly equal to a depression of T 3 g- of an inch of mercury in the 

 same place, or a rise of that quantity where the water is held 

 in solution, as was the case at Boston. 



The area of my pluviameter is 6 square inches, and the 

 weight of 3^ inches depth of rain in that square, allowing 20 

 ounces avoirdupois to a perpendicular inch, is 4lbs, loz. In 

 the area of 6 square inches are contained 36 square inches, 

 being the square of six, and by dividing 4lbs. loz. by 36, the 

 quotient is loz. 14§drs. Assuming the pressure of the incum- 

 bent atmosphere to be 15 pounds weight upon every square 

 inch of surface at the level of the sea, the following proportion 

 may be adopted for ascertaining the additional pressure at 

 Boston over that at Gosport on the 14th of last May, after an 

 exhaustion of 34, inches of rain in the latter place more than 

 in the former. 



As 15lbs., the weight of the atmosphere on a square inch of 

 surface, is to the mean altitude of the barometer, 30 inches ; 

 so is loz. 14fdrs., to # 24 inch of mercury, which is within *06 

 inch of what Mr. Veall's barometer indicated too much at that 

 time. My barometer is fixed 50 feet above low-water mark. 



It now remains for Messrs. Can and Veall to make any ad- 

 Vol. 61. No. 317- Sept. 1824, Dd ditional 



