POINT OF SOLAR ACTION. 45 



and that while the daily change just at the equinox is 

 about twenty- three miles in a day, that just at the 

 tropic is not one-tenth of a mile. 



Thus the motion of the point of greatest solar influ- 

 ence through the quarter that extends from our winter 

 tropic, or solstice, to our vernal equinox, might be re- 

 presented by a line or thread wound about ninety times 

 round the globe from east to west, having its beginning 

 in the parallel of 23 28' south latitude, and the termina- 

 tion at about the ninetieth round somewhere in the 

 equator. Toward the tropic the rounds will be very 

 near to each other ; and their distance will gradually 

 increase, till at the equator, or just before the equinox, 

 it will be more than three hundred times as much as 

 at the tropic. 



Crossing the equator some time on the 2 1st of March, 

 the point will continue its daily revolutions into the 

 northern hemisphere, the spaces between the daily 

 rounds becoming less and less as they extend toward 

 the north ; and when about ninety-two rounds have been 

 completed, the sun will appear to be vertical at some 

 point on the northern tropic or parallel of about 23 28' 

 north. By this time, another quarter of the year will 

 have thus passed away, and it will be midsummer in 

 the northern hemisphere. It is not necessary to trace 

 the motion through tUe remaining half of the year, 

 because the only difference is a daily deviation south- 

 ward, which is small at the beginning, increases toward 

 the middle, and again diminishes toward the end, till, 

 after the revolution of a whole year, marked out by 

 about 365jf: spiral traces, winding from east to west, 

 one half of them inclining north and the other half 



