Petersham, Mass., August 25, l9g«>. 



Mr. leane, 

 PhiJL brook Farm, 

 Shelburne, K.H. 



Dear Mr. Beane: 



Yes, the days at the equator are always practically 

 equal to the mights. 



Refraction raises the sun at the horizon about two 

 minutes so that we see it about 2 minutes before we should 

 if there were no atmosphere; at sunset 2 minutes after we 

 should lose sight of lit if there were no atmosphere. 



This applies to the centre. It takes about a min- 

 ute more for the upper edge to set so that we get some light 

 f»r about that amount of time at each end of the day — - a few 

 seconds more on Jan. 1, than on July 1 because the sun is 

 nearer on Jan 1, and its apparent diameter is greater. 



Refraction always lengthens the day about 4 minutes 

 and semidiameter about 2 minutes so that the day is about 12 

 hours and 6 minutes and the night 11 hours and 54 minutes. 



I will explain in Cambridge and also tell you of 

 the effects of parallax, a few seconds in diminishing the 

 day; and the equation of time^also small and variable with 

 the time of year. 



Sincerely yours, 



