We will now make the calculation for the central vortex _descending_, for longitude 88° 50′ west, August 7, 1853,--putting down the necessary elements for the time of the meridian passage in order: Meridian passage in local time at 2h. 25m. P.M. " " in Greenwich time 7d. 8h. 18m. Mass of the moon 1/12.3 M. R. V. minor 3,256 miles. Obliquity of the vortex, same time 26° 5′ 0″ Polar angle of " " 17 41 47 True longitude of moon's node " 78 42 0 " inclination of orbit " 5 5 0 " longitude of the sun " 135 20 0 Moon's longitude " 169 44 0 " distance from node " 91 2 0 " distance from quadrature " 55 36 0 " true semi-diameter " 943 " right ascension " 172 30 0 " declination north " 8 42 20 Constant logarithm 2.889214 Arith. comp. of log. of 943 7.025488 Log. cos. arc. AR 9.914702 = 34° 44′ 48″ 1st. correction, + 2 45 0 2d. correction, - 1 14 15 -------------- Corrected arc AQ = 36 15 33 PA = 81° 17′ 40″ PV = 26 5 0 P = 115 11 47 V = 63 34 26 A = 23 28 24 AV = 92 48 39 Q = 31 32 18 Complement of lat. = PQ = 48° 49′ 41″ The latitude is therefore for the earth, as a sphere 41 10 18 Correction for protuberance + 0 16 0 ------------ True latitude of centre 41 26 18 north. ------------ Latitude of Ottowa 41 20 0 " ------------ Vortex passed 6 18 north of Ottowa. [Illustration: Fig. 16] As this was nearly a central passage, and as the influence was less extensive than usual, on account of great atmospheric pressure with a low dew point, the central disturbance could the more readily be located, and was certainly to the north, and but a few miles. The following is from the record of the weather: _August_ 6th. Very fine and clear all day; wind from S.-W.; a light breeze; 8 P.M. frequent flashes of lightning in the northern sky; 10 P.M. a _low bank of dense clouds in north_, fringed with cirri, visible during the flash of the lightning; 12 P.M. same continues.