452 



PHILOSOPHICAL TRANSACTIONS. 



[anno i6q\. 



In the month of April. 



The transits marked with the sign * are partly visible at London, but those 

 with the sign * * are entirely to be seen there. 



Note, that the sun's diameter at the ascending node of Mercury, in the 

 month of October, is 32' 34" ; and therefore that the greatest duration of the 

 central transit is 5h. 29m. ; but in April the sun's diameter becomes 3 1' 54* ; 

 whence, on account of the slower motion of the planet, the greatest duration 

 is 8h. Im. But if Mercury should fall obliquely on the disk, these durations 

 become shorter, in proportion to the distance from the sun's centre. But, that 

 the calculus may be the more perfect, the following tables are subjoined, wherein 

 are exhibited the half durations of these eclipses for each minute of distance 

 seen from the sun's centre ; which added to, and subtracted from, the moment 

 of conjunction found in the former table, exhibit the beginning and end of the 

 whole phenomenon. 



