ASTRONOMICAL OBSERVATORIES. 247 



gave two hundred and fifty, and another gave two hun- 

 dred dollars. 



The Corporation of Harvard University purchased an 

 excellent site for the erection of an observatory. The 

 ground comprises about six and a half acres. The posi- 

 tion is elevated about 50 feet above the general plain on 

 which are erected the buildings of the University ; and 

 it commands in every direction a clear horizon, without 

 obstruction from trees, houses, smoke, or other causes. 

 Upon this spot, which is known as Summer House Hill, 

 the Sears Tower was erected for the accommodation of 

 the large telescope, with wings for other instruments, 

 and a house for the observer. The Sears Tower is a 

 brick building 32 feet square, resting on a granite found- 

 ation. The corners of the towers are arched so as 

 gradually to bring the interior into a circular form of 31 

 feet diameter, surmounted by a granite circle, on which 

 is laid an iron rail hollowed in the middle to serve as a 

 track for the iron balls on which the dome revolves. 

 The dome has a diameter of 30 feet on the inside, with 

 an opening five feet wide, extending beyond the zenith. 

 The shutters to this opening are raised and closed by 

 means of endless chains working in toothed wheels. To 

 the lower edge of the dome is affixed a grooved iron 

 rail similar to the one laid on the granite cap of the 

 walls, and the dome rests on eight iron balls, which had 

 been smoothly turned, and were placed at equal dis- 

 tances round the circle. Although this dome is es- 

 timated to weigh about fourteen tons, yet it can be 



