ASTRONOMICAL OBSERVATORIES. 215 



In the year 1838 a tower, about 45 feet high, was 

 erected in the rear of the school building, and was in- 

 sulated 10 feet below the surface of the earth. The brick 

 walls were three feet thick at bottom, and two and a half 

 feet thick at top, and the diameter of the tower was 

 about 12 feet in the clear. It was surmounted by a 

 dome 18 feet in diameter, weighing about two tons. The 

 telescope rested on two marble slabs, each weighing about 

 a thousand pounds, which were supported by two strong 

 cast-iron beams that reached from the north to the south 

 brick wall, and thus bound the two walls together. 



The equatorial, by Merz and Mahler, of Munich, is of 

 eight feet focal length, and six inches aperture, with 

 clock-work movement. The hour circle is nine inches 

 in diameter, reading to four seconds of time ; the declina- 

 tion circle is 12 inches in diameter, reading to ten seconds 

 of arc. This telescope is mounted like the celebrated 

 telescope at Dorpat, and has a variety of powers to 480, 

 with micrometers. 



The meridian circle is by Ertel, of Munich, and was 

 mounted on marble pillars resting on the south wall of 

 the tower. The telescope has an object-glass of five 

 feet focal length, four and a half inches aperture, and is 

 so constructed that the object-glass and eye-glass may 

 be made to change places. It has two circles, each 

 graduated to read by the aid of four verniers to two 

 seconds of arc. The clock is by Lukens, and has a mer- 

 curial pendulum. The cost of the several instruments 

 was as follows: equatorial telescope, $2,200; meridian 



