Proceedings of the Polytechnic Association. 849 



Moon, as so many parts of the solar system. It represents the motion 

 of the sun on his axis ; the relative yearly motions of Mercury, Venus 

 and earth ; also their relative daily motions, and the motions of the 

 moon around the earth, around the sun, and on her axis. It shows 

 the inclination of the axes of Yenus and the earth to the planes of 

 their orbits, and illustrates the respective widths of their diiferent 

 zones ; the succession and duration of their different seasons ; the dif- 

 ferent l-engths of their days and nights ; the amount of change of the 

 sun's declination in relation to each, and his rising and setting on 

 each ; the superior and inferior conjunctions and phases of Mercury 

 and Venus, also the solar and lunar eclipses ; the length of lunar 

 days and nights ; the retrogression of the moon's nodes, and the 

 changes, phases, and fulling of the moon. 



By the use of the Ileliotellus and the artificial zodiac connected 

 therewith, these phenomena, the tides also, and other elements of 

 useful knowledge, can be explained with such clearness and simplicity 

 that even a child, with little attention, cannot fail to comprehend 

 them, Tliis instrument, for the purpose of illustrating a portion of 

 the planetary system and the phenomena resulting therefrom, is 

 invaluable ; and as it can be carried in the hand, and occupies but 

 little space, economizes the time and expense of the pupil, and dimin- 

 ishes the labor of the teacher. The price of this instrument is forty 

 dollars. 



LUNATELLUS. 



Mr. Whitall also exliibited a Lunatellus, which illustrates the 

 astronomical phenomena of tlie sun, earth and moon in their natural 

 order ; with the geography of the earth in its proper relation to them. 

 The sun is made to turn on his axis ; the earth revolves at her 

 proper inclination on her axis and around the sun, producing not 

 only the change of seasons, and the vicissitudes of day and niglit, but 

 also their natural increase and decrease in. length. The moon revolves 

 around the sun on her axis, and around the earth, producing the 

 alternation of her days and nights ; her changes, phases and fulling, 

 and also by her retrograding at every revolution and the interesting 

 phenomena of solar and lunar eclipses. And as the natural divisions 

 of the surface of the earth, and political divisions of every country 

 are marked on the body that is employed to represent the earth, the 

 geographical and astronomical relations of every locality, at any 

 particular period during the year, are clearly exhibited to the eye. 

 This instrument is sold at sixty dollars. 



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