94 Memoir relative to the Annular Eclipse of the Sun 



selves. 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 geography. 



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 : 

 I allude to the formation and dissolution of the annulus*. This 

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

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

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

 with a glass smoked in the manner hereafter mentioned J. The 

 times of these phases may be determined with sufficient accuracy 

 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 appear- 

 ance; which will be the same, whether the watch is right or not§. 

 As the method therefore of observing this phaenomenon is so 

 simple and easy, it is hoped that no person, to whom the oppor- 

 tunity may occur, will omit to note down the particulars ; or fail 

 to communicate the same to some person conversant with the 

 subject of astronomy. It will be of equal importance to know 

 that the existence of the annulus is only momentary : or even that 

 it is nearly, but not completely formed || . 



Although the possession of proper instruments must give a su- 

 perior degree of credit to the observations of any person ; yet I 



would 



* The annulus is considered hs coniplcttly/onnerf when tlic whole body 

 of the moon just appears on the disc of the $um, however unequal in breadth 

 the uncovered part of the suns disc may he. It is considered as dhsolved 

 the :noment the moon ayain 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. 



■f A common opera gla?:. might be made use of, if nothing better should 

 present itself: as no method should remain untried for determining this vciy 

 important phase. If the observer he near-sighted, and have not the advan- 

 tage either of telescope or concave glasses, he may view the sun through 

 a small hole made in a card by means of a pin. 



X Those, who cannot procme cither coloured or smoked glass, may view 

 the image of the sun in a bucket of water, or a vessel filled with oil, placed 

 in a situation where it may not be agitated by the wind. 



§ Should the ob;,ervcrbe in such a situation as not to have the advantage 

 of either a clock, or a watch beating seconds, he might easily make a tem- 

 porary pendulum, of any convenient length, and notice the number of vi- 

 brations which it makes during the existence of the anniiius. In such case, 

 the length and substance of the pendulum should be specified. 



Il To those who are not much conversant with practical astronomy, it may 

 perhaps be proper to remark, that the more numerotu these observations 



may 



