s 



1818.] Annular Eclipse of the Sun. 183 



great part of Asia and Africa, the eclipse will be visible ; differ- 

 ing only in magnitude according to the situation of the spectator. 

 But, in no part will it be annular except at those places which are 

 situated within the limits of the umbra, as above-mentioned.* 



Those persons who happen to be situated on the western 

 border of the umbra will, at the time of the middle of the eclipse, 

 see the upper limb of the moon in contact with the upper limb 

 of the sun ; and consequently the unobscured portion of the sun's 

 disc will be seen round the under part of the moon. On the 

 contrary, those persons who are on the eastern confines of the 

 umbra will see the lower limb of the moon in contact with the 

 lower limb of the sun. Whilst to those who are stationed 

 directly in the central path, the centres of the sun and moon 

 will appear exactly to coincide ; and an uniform luminous ring, 

 equal in breadth to about ^ part of the sun's diameter, will 

 surround the body of the moon.t 



As there are no two points on the face of the globe where the 

 visible appearances of any solar eclipse are exactly alike, it 

 would be an endless task to compute the phenomena for any 

 considerable number of places ; and the usual mode amongst 

 astronomers is to give a general outline of the path of the moon's 

 shadow, and to calculate the particular circumstances of the 

 eclipse for the metropolis only, or for some known observatory ; 

 which calculation may be easily adapted to other parts of the 

 kingdom. The notices which are given in the various 'epheme- 

 rides on this point are merely for the purpose of informing 

 astronomers to look out for, and note down these phenomena ; 

 and the observations thus made are afterwards collected and 

 compared together. Under these circumstances the reader 

 must not expect to find the exact time and appearances of this 

 eclipse computed for every place on the continent. It will be 

 sufficient for his purpose if he knows at what time of the day he 

 ought to look out _for its commencement, and at what point of 

 the sun's disc he ought to fix his attention in order to observe 

 the first point of contact. The following table will show nearly 

 these several particulars for the different places therein men- 

 tioned ; and will assist the observer in his computations for any 

 other place within the umbra. These values are deduced 

 merely from a projection of the eclipse, and are consequentlv 

 given as approximations only, and by no means as the exact 

 values ; for, where it is required to have the time true to the 

 nearest second, the observer must calculate the phases of the 

 eclipse for the precise spot where he happens to be stationed, 

 i lie angles from the vertex are all reckoned on the right hand 



* In order to give a general view of the path of the umbra across the continent 

 of Eorope, a map of (he same (I'late LXXXV) will be given to accompany tiie 

 remainder of the paper in our next number. 



+ The sun will be elevated on thai day above the horizon about S4 degrees to 

 that part of the continent over which the centre of Ibe union's umbra passes; con- 

 sequently the increase of tin- mooo'i Bemidiameter will be about 7] seconds. 



