8 



ASTRONOMY. 



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any part of it to wlilch the attention of navigators sliould 

 be specially directed with a view to its improvement. 



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rhaps the principal deficiency at the present time is in 

 the want of weli-unilerstood methods of observing (with 

 the sextant) the altitudes of stars at night, and of observ- 



ing the altitudes of the sun and moon when the horizon is 

 ill'definede Every endeavour ought to be made to become 

 familiar with the use of BecherV horizon, or some equi- 

 valent instrument, and to acquire a correct estimate of the 

 degree of confidence which can be placed in the use of it. 

 9. It is likewise desirable that efforts should be made 

 to facilitate the observation of occultations of stars by the 

 mooo, and the observation of eclipses of Jupiter s satellites 



at sea. O 



but the result whic! 



I 



they give for longitude is usually so much more accurate 

 tlian that given by lunar distances, that, in long vovages 



where little dependence can be placed on the chronometer, 



n occultation must be extremely 



the observation 





valuable. The eclipses of Jupiter's satellites afford less 

 accurate determinations of longitude^ but they occur very 

 much more frequently, and may be very useful where 

 chronometers cannot be trusted.* 



* Attemptf. may laudably be made to deyise some available mode of 

 suspending a chair, :^o as to afford a steady seat to the observer. Hitherto 

 such attempts have failed of practical success, from setting out with the 

 principle of perfectly free suspension, a principle -^hich tcnd6 to prolong 

 and perpetuate oscillations once impressed. It remains to be seen what 

 stiff suspensioii, as for example by a rigid rop^ or cable, or by a hook's 

 joint, purpose'.^. iix:.C.^ to work stiffly (and that more or less at pleasure), 

 by tightening collars — as also deadening and shortening oscillations, by 

 iatf-ral cords passing through m/.7i- to create friction — and other similar 

 contrivances may do. In the suepeasioa of a cot> at leastj I have found 

 this principle signally available.— (Ed. 1 



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