110 BENJ. PIKE'S, JR., DESCRIPTIVE CATALOGUE. 



of the place you are considering is above the horizon, and 

 then the circles on the sphere will, with respect to the globe 

 within it, correspond with the imaginary circles of astrono- 

 mers in the heavens. 



The Hour Circle is a small circle fixed about the north 

 pole, with a hand on the axis of the sphere, so that by turn- 

 ing the sphere on its axis the index will be carried round the 

 circle. 



This circle is used to convert the degrees of the equator 

 into time ; it is divided into twenty-four equal parts, answer- 

 ing to twenty-four hours, or the time of an entire revolution 

 of the heavens. The index, by pointing successively to those 

 hours, shows in what space of time any part of that revolu- 

 tion is performed. 



The Quadrant of Altitude. This is a long slip of brass 

 with a nut at top to fix it to the meridian ; it is divided into 

 ninety degrees, and being fixed at the zenith it reaches to 

 the horizon ; it may be carried to any part of the sphere, 

 and thus will show the height or altitude of any point above 

 the horizon in any position of the sphere. 



Price, best 13 inch diameter, $40.00. 



" plain, $20.00 and $25.00. 



" common fig., 9 inch, $ 4.00. 



" 12 " $ 5.00. 



Planetarium. (Fig. 122, next page.) A planetarium 

 may be considered in some sort as a diametrical section of 

 our universe, in which the upper and lower hemispheres are 

 suppressed. 



The upper plate is to answer for the ecliptic ; on this are 

 placed, in two opposite but corresponding circles, the days 

 of the month, and the signs of the ecliptic, with their res- 

 pective characters ; by this plate you may set the planetary 

 balls so as to be in their respective places in the ecliptic, for 

 any day in the year. 



Through the centre of this plate, you observe a strong 

 stem, on which is a brass ball to represent the sun ; round 

 the stem are different sockets to carry the arms, by which 

 the several planets are supported. The planets are repre- 

 sented by white or gilt balls. We can with ease either take 

 off, or put on, any of the planets, as occasion may require. 

 About the primary planets are placed the secondary planets 



