1835.] Observations on the value of the cipher, §^c. 371 



= infinity, divide both sides of the equation by 0 and 



, X iunnity 



but Ox 0 0 infinity = '""^^ or 0 = 1 

 multiplying the equation by ^r, 0 = x. 

 thus from the foregoing instances we see that a cipher, 

 or nothing has after all some particular value of itself^ 

 and is therefore far from being quite so insignificant as 

 it is generally considered. 



No. II.- — On computing the time of the Moon's 

 rising and setting. 



It was not my intention to have presented you with 

 more than one article this time, but after I had dis- 

 posed of my subject of the cipher I felt as if I had 

 rather have devoted my time to a more congenial sub- 

 ject^ and so without further ado I set about preparing 

 the following observations : 



It invariably happens that all echpses of the Moon 

 are visible in some part of the earth when the Sun and 

 Moon are both above the horizon ; hence the uninitiated 

 observer v/ould at first sight be led to consider the hypo- 

 thesis of eclipses as erroneous, yet if he should extend 

 his enquiries into the laws of refraction and other cir- 

 cumstances connected with this phenomenon^ he will be 

 convinced that his suspicions are groundless. 



There will be an eclipse of the Moon on the 24th 

 October, 1836, which we may expect to be visible here 

 immediately before sun-set : as this cannot but be an 

 interesting phenomenon to many, I have endeavoured 

 for their convenience to investigate a formula for com- 

 puting the times of the Moon's rising and setting, which, 

 I believe, will be acceptable to such as may need its 

 assistance on the occasion. 



The mean time of the transit of any heavenly body is 

 expressed by the difference between the right ascensions 



