GLOBE. 



ecliptic opposite to the sun's place ; by 

 the present problem it may be shown 

 what places of the earth; then see the mid- 

 dle of the eclipse, and what the beginning 

 or ending, by using the moon's place in- 

 stead of the sun's place in the problem. 



17. " To find the bearing of one place 

 from another, and their angle of position." 

 Bring the one place to the zenith, by rec- 

 tifying the globe for its latitude, and turn- 

 ing the globe till that place come to the 

 meridian ; then screw the quadrant of al- 

 titude upon the meridian at the zenith, 

 and make it revolve till it come to the 

 other place on the globe ; then look on 

 the wooden horizon for the point of the 



t compass, or number of degrees from the 

 * south, where the quadrant of altitude cuts 

 it, and that will be the bearing of the lat- 

 ter place from the former, or the angle of 

 position sought. 



18. " The day and hour of a solar or 

 lunar eclipse being given, to find all 

 those places in which the same will be 

 visible." Find the place to which the 

 sun is vertical at the given instant ; and 

 elevate the globe to the latitude of the 

 place ; then, in most of those places 

 above the horizon will the sun be visible 

 during his eclipse ; and all those places 

 below the horizon will see the moon pass 

 through the shadow of the earth in her 

 eclipse, 



19. " The length of a degree being gi- 

 gen, to find the number of miles in a 

 great circle of the earth, and thence the 

 diameter of the earth." Admit that one 

 degree contains 69 \ English statute miles; 

 then multiply 360(the number of degrees 

 in a great circle) by 69 and the pro- 

 duct will be 25,020, the miles which mea- 

 sure the circumference of the earth. If 

 this number be divided by 3.1416, the 

 quotient will be 7,963_ 8 6 miles, for the 

 diameter of the earth. 



20. " The diameter of the earth being 

 known, to find the surface in square miles,' 

 and its solidity in cubic miles." Admit t 

 the diameter be 7,964 miles ; then multi- \ 

 ply the square of the diameter by 3.1416, 

 and the product will be 199,250,205 very 

 near, which are the square miles in the 

 surface of the earth. Again, multiply the 

 cube of the diameter by 0,5236, and the 

 product 264,466,789,170 will be the num- 

 ber of the cubic miles in the whole globe 

 of the earth. 



21. " To express the velocity of the 

 diurnal motion of the earth." Since a 

 place in the equator describes a circle of 

 25,020 miles in twenty-four hours, it is 

 evident that the velocity with which it 



VOL. VI. 



moves is at the rate of 1,042 in an hoili*, 

 or 17-^. miles per minute. The velocity 

 in any parallel of latitude decreases in 

 the proportion of the co-sine of the lati- 

 tude to the radius. Thus for tbe latitude 

 of London, 51 30', say, 



As radius ...... - 10.000000 



To the co-sine of lat. 51 30' 9.794149 

 So is the velocity in the equa- ? 2 238046 



tor, 17^ - - - - 5_ _ 

 To the velocity of the city of ? 5 



London, 10_ - - 5 



That is, the city of London moves about 

 the axis of the earth at the rate of 10_ 8 -j. 

 miles every minute of time : but this is 

 far short of the velocity of the annual 

 motion about the sun ; for that is at 

 the rate of more than 65,000 miles per 

 hour. 



PROBLEMS OST THE CELESTIAL GLOBE. 



1. "To rectify the globe." Raise or 

 elevate the pole to the latitude of the 

 place ; screw the quadrant of altitude in 

 the zenith ; set the index of the hour- 

 circle to the upper xn ; and place the 

 globe north and south by the compass 

 and needle ; then is it a just representa- 

 tion of the heavens from the given day at 

 noon. 



2. To find the sun's place in the eclip- 

 tic." Find the day of the month in the 

 calendar on the horizon, and right against 

 it is the degree of the ecliptic, which the 

 sun is in for that day. 



3. " To find the sun's declination." 

 Rectify the globe, bring the sun's place 

 in the ecliptic to the meridian, and that 

 degree which it cuts in the meridian is 

 the declination required. 



4. " To find the sun's right ascension.*' 

 Bring the sun's place to the meridian, 

 and the degree of the equinoctial cut by 

 the meridian is the right ascension re- 

 quired. 



5. "To find the sun's amplitude." 

 Bring the sun's place to the horizon, and 

 the arch of the horizon intercepted be- 

 tween it and the east or west point is the 

 amplitude, north or south. 



6. K To find the sun's altitude for any 

 given day and hour." Bring the sun's 

 place to the meredian ; set the hour-in- 

 dex to the upper xn ; then turn the 

 globe till the index points to the given 

 hour, where let it stand; then screwing 

 the quadrant of altitude in the zenith, 

 lay it over the sun's place, and the 



D 



