THE EARTH AS A PLANET 189 



sun and moon from the observer ; (e) through which quarter 

 of its revolution about the earth the moon must have passed 

 when seen in the morning as a half moon; (/) to which 

 phase the moon comes at the end of the fourth quarter; 

 (g) why the moon is not then to be seen for a time. 



4. With the moon full and rising at sunset, what is the 

 position of the earth with reference to the sun and moon? 

 At time of "dark moon," which side of the moon as lighted 

 by the sun is towards us? What kind of a body must the 

 moon be with reference to giving off light of its own? 



5. When the moon was new, what was its place of setting 

 relative to that of the sun? What was true in this respect 

 when the moon was full? 



6. How many full moons may there be in a year? Ac- 

 count for the "months" of our calendar. Ascertain the 

 relation of the date for Easter in any year to the time of full 

 moon then. 



TIME AND TIME-KEEPING, AND STANDARD TIME 



1. With a string and any suitable weight arranged to 

 swing freely from a fixed point of support as a pendulum, 

 and with the length from the point of support to the center 

 of bob about 25 inches, set the pendulum swinging through 

 a small arc, and count the number of oscillations per minute. 

 Repeat, with the pendulum length (a) less; (b) greater. 

 Upon what does the time for one oscillation seem to depend ? 



2. Make the pendulum length now 36 inches, and count 

 the number of oscillations. Find the ratio value to two 

 decimal places (a) of the numbers of oscillations for the two 



