ASTRONOMICAL INSTRUMENTS. 115 



shows in an accurate and clear manner the phenomena 

 arising from the annual and diurnal motion of the earth ; the 

 change of the seasons ; the revolution of the moon round 

 the earth, moving in an orbit inclined to that of the ecliptic, 

 and illustrating the subject of eclipses. The gilt ball repre- 

 senting the sun can be taken off, and a lamp substituted in 

 its place, illuminating the earth in one hemisphere only, and 

 the moon differently in its various positions. There are 

 four distinct motions given to this instrument, three by 

 means of wheels with cords passing round them, and one 

 with toothed wheels, also a screw at the end to tighten the 

 cords when required ; the globe is three inches in diameter, 

 and all the continents, seas, etc., may be distinctly seen ; 

 the equator, the ecliptic, tropics, and other circles, are very 

 visible, so that problems, relative to particular places, may 

 be satisfactorily solved ; the axis of the earth is inclined to 

 the ecliptic in an angle of 66^ degrees, and preserves its 

 parallelism during the whole of its revolution ; when the 

 north pole is turned directly towards the sun, the globe is 

 in the position of the earth for the longest day in our 

 northern hemisphere, or the 21st of June ; turn the handle 

 of the instrument till the earth and moon have revolved 

 half round the sun, and the north pole is directed from the 

 sun, and we have the shortest day, or the 21st of December; 

 there are two intermediate positions in the revolution of the 

 globe, answering to the positions on the 21st March and the 

 21st of September, when the two poles are equally exposed 

 to the sun, and when the days and nights are of a length 

 all over the earth. The phases of the moon are clearly ex- 

 hibited by this instrument. When the moon is between the 

 earth and the sun, we call it new moon, the enlightened 

 part being then turned from us ; but when the earth is be- 

 tween the sun and moon, we call it full moon, the enlight- 

 ened part being then turned towards us; in the intermediate 

 positions we have the first and last quarter of the moon. 

 Price, on brass stand, $13.50. 



" on mahogany stand, $7.00. 



Eclipse Instrument. (Fig. 126, next page.) This instru- 

 ment consists of a painted ball of four inches in diameter, 

 representing the sun, mounted on a mahogany base twenty 

 inches long ; there is supported from each end a two inch 

 terrestrial globe ; to the axis of one of these is supported a 



