250 Mr. Baily on an [Oct. 



observed in former eclipses of this kind,* whereby the reader 

 may be aware of the principal observations to which it will be 

 proper for him to attend, and make his preparations accordingly. 

 Many of these phenomena have given rise to much discussion, 

 and are far from being accurately determined, or reduced to 

 general principles. There is also a degree of doubt respecting 

 the existence of some of them. Those persons, therefore, who 

 are furnished with convenient instruments, and have a favourable 

 opportunity, should carefully attend to, and note dcwn, not 

 merely the phases of the eclipse, but such other appearkaces as 

 may present themselves. It is only by multiplying observations 

 of this kind that we can ultimately arrive at the truth : and an 

 annular eclipse is so rare an occurrence in this part of the globe, 

 that it is hoped every advantage will be taken of it, to improve 

 and advance the connected sciences of astronomy and geo- 

 graphy. 



There is one important observation, however, connected with 

 this eclipse, which it is in the power of almost any competent 

 person to make, without the aid of any particular instruments : 

 1 allude to the formation and dissolution of the annulus .f This 

 may be determined very accurately, if not by the naked eye, at 

 least with a telescope of very small magnifying power ; % fur- 

 nished with a coloured glass to keep off the rays of the sun, or 

 with a glass smoked in the manner hereinafter mentioned.^ The 

 times of these phases may be determined with sufficient accu- 

 racy by means of a clock, or watch that beats seconds ; and 

 which should, if possible, be set to mean time on the day of the 

 eclipse. The neglect of this precaution, however, should not 

 prevent the observer from noting down the duration of the 

 annular appearance; which will be the same, whether the 

 watch is right or not. |j As the method, therefore, of observing 

 this phenomenon is so simple and easy, it is hoped that no 



» Those of 1731 and 1748. There are but few observations of the eclipse of 

 1764. 



+ The annulus is considered as completely formed when the whole body of the 

 moon just appears on the disc of the sun, however unequal in breadth the unco- 

 vered part of the sun's disc may be. It is considered as dissolved the moment the 

 moon again touches the concave circumference of the sun's disc. The duration of 

 the annulus will not in any place, as already observed, exceed six minutes, and in 

 some places will be momentary. 



\ A common opera glass might be made use of, if nothing better should present 

 itself: as no method should remain untried for determining this very important 

 phase. If the observer be near-sighted, a_nd have not the advantage either of a 

 telescope or concave glasses, he may view the sun through a small hole made in a 

 card by means of a pin. 



(j Those who cannot procure either coloured or smoked glass may view the 

 imnge of the sun in a bucket of water, or a vessel filled with oil, placed in a situa- 

 tion where it may not be agitated by the wind. 



j| Should the observer be in such a situation as not to have the advantage of 

 either a clock, ot a watch beating seconds, he might easily make a temporary pen- 

 dulum, of any convenient length, and notice the number of vibrations which it 

 makes during the existence of the annulus, In such case, the length and substance 

 of the pendulum should be specified. 



