88 ASTRONOMY. 'i 



i 

 i 



terns of signals which extend only so far as to communicate j 

 intelligence of events which have been foreseen, and the | 

 appropriate signals, previously arranged, are called signal ] 

 flags, signal lanterns, and signal guns or fires. Telegraphs ] 

 have been constructed in various ways. What is called the ] 

 English telegraph consists of six octagonal boards, each of ] 

 which is poised upon an axis in a frame, and worked by : 

 means of ropes in the manner of bell-ropes, so that it can ; 

 either be placed vertically, and appear with its full size to ^ 

 the observer at the nearest station, or it becomes invisible to j 

 him by being placed horizontally, so that the narrow edge j 

 alone is exposed, which from a distance cannot be seen. | 

 Six boards make thirty-six changes, by the most plain and | 

 simple mode of working ; and they will make many more, if | 

 more were necessary ; but as the real superiority of the te- ^ 

 legraph, over all other modes of making signals, consists in 'j 

 its making letters, it is not necessary that the changes should j 

 be more than the letters of the alphabet, and the arithme- J 

 tical figures. Telegraphs of this description are set up on 1 

 eminences at the distance of eight, ten, or twelve miles ; | 

 and a line of them, by repeating each other's signals, conrj 

 veys a message at the rate of a hundred miles in about five j 

 minutes. A telescope for the use of the observer is fixed ^ 

 in the watch-tower of each station. "I 



Questions. — 1. Of what advantage is the telescope ? 2. Why does I 

 it seem to bring an object nearer ? ^. What is said of the eye-glasses M 

 and the magnifying power of telescopes ? 4. Why are mirrors usedj 

 in reflecting telescopes ? 5. Describe the Newtonian telescope. 6.| 

 Describe the telescope as made by Dr. Herschel. 7. His grand tele- 1 

 scope. 8. What is a telegraph.^ 9. How is a proper telegraph dis-' 

 tinguished from other machines for making signals ? 10. Describe »; 

 the English telegraph. 11. What is said of its number of changes ?^ 

 12. At what rate will such telegraphs convey a message ? 13. How | 

 may an idea of the Newtonian telescope be obtained by looking at ^ 

 fig. 27. 1 



LESSON 40. - 



I 

 Astronomy. - 



Locomo'tive, having the power of removing, or changing place. .'^ 



Astronomy is the science which teaches the magnitudes^ 



and motions, distances, periods, and order of the celestia.l| 



