TIIK SrXDIAT. AND TIIK CLOCK. 109 



the same conventional system, are permanently separated from 

 each other. Now the true sun beinjj- sometimes ahead of these 

 mean solar points and sometimes behind them, he must be 

 with them, with the one or the other, at certain periods of the 

 year ; — in fact at four periods of the year, as shall be shown. 



The equation of time is to be added algebraically to mean 

 solar time in order to keep it with the sun. 



Generally, therefore, on those days only when the equation 

 of time added with the proper sign to mean solar time makes 

 the same equal to standard time, will standard time, which we 

 carry and not local mean solar, agree with sun time. 



As to the proper sign. L,et it be remembered that those 

 who live to the eastward of the bisecting meridian must sub- 

 tract from local mean solar to get standard time ; those who 

 live to the westward must add. 



But it is only when the clock is ahead of the sun that local 

 mean solar may be drawn down automatically, so to speak, to 

 agree with standard, that the standard watch can agree with 

 the sun. That is to say while the clock is " fast " ; so that 

 those living to the eastward of the bisecting meridian add 

 with the same sign and all dates of agreement between stan- 

 dard and sun will fall to the " clock fast " side. 



On the contrary it is only when the clock is behind the 

 sun that local mean solar may be brought up automatic- 

 ally so to speak to agree with standard, that the standard 

 watch can agree with the sun. That is to say, while the 

 clock is "slow." So that those living to westward of the 

 bisecting meridian, add with the plus sign, and all dates of 

 agreement between standard and sun fall to the " slow " side 

 of the vertical. 



I am now going to try your patience ; — for a few minutes, 

 only, however, by inquiring minutely what goes on in this 

 connection at about 40° north and 75° 23' W. of Greenwich. 

 In short at Media. What is said will apply to any other point 

 in the U. S. if the proper change of data be made. And I 

 shall have to sav the same thing more than once. 



