234 A Companion to the Moon Table. [No. 135. 



The division lines and marks on the three cards being not continu- 

 ous in these as in the week-day table, a silk thread is attached to 

 them, in order to facilitate the bringing of the proper marks on the 

 cards correctly into line. With the same view, the month marks 

 have been projected on the circle separating the months and days. 

 These marks are so small, as not to attract attention unless particular- 

 ly looked for. 



The method of using and manipulating these moon tables is so 

 perfectly analogous to that formerly detailed The mon th marks on the inner 

 for the week-day table, that beyond the 

 directions on the face of the cards, nothing 



January 



more seems necessary. An example or two ^rch" 7 ' " 



may suffice. Required true time of full ^ p a ri1, 



moon in October 1841, the 18 on the outer Jj^' ;;;;;;; 



circle of the middle card being set to ## on September,' 



Common. 



O'OO 



48-12 

 47-24 

 40-36 

 45-48 

 68*60 

 23-72 

 16-81 

 Srffl 

 5-08 

 .*3-20 

 48-32 



Leap. 



2-00 



50*12 



the outer, and the mark for October brought November,' 

 in line with that for the current year 41; ecem er "' 

 the full moon mark O falls almost exactly on the line between 29 and 

 30, hence the time of mean full moon is on the 30th at Oh. a. m. For 

 this date, the back of the Companion gives 4.18h. to be subtracted : 

 then for 1841 October, 29d. 8h. p. m. the face of the Companion gives 

 9.47h. to be added : the time of true full moon is thus the 30th at 

 5h. 29m. a. m. To which adding 5h. 54m. as the diff. of longitude 

 between Greenwich and Calcutta, we get 30d. llh. 23m. a. m. as 

 the time at Calcutta. I have not at present the means of comparing 

 with the Nautical Almanac, but the old tables, supposed to be 

 Ferguson's, give 30d. Oh. 03m. 31s.* the difference being about 

 40 minutes. 



An Eclipse of the sun is said to have been seen at Babylon in 

 March 721, B. C. =8-80 O.S.Now 8, being set to ##, and March inline 

 to 80, mean new moon was about 20d. 2h. a. m. 721 1 q3 80Q == 24.5, to which 

 add 12 days for diff. of styles and 20th March+36 is 5th April, for 

 which date the first Equation is-f-4.08m. and this applied to 20d. 

 6h. gives 20d. 6h, 08m. a. m. and for this date year 8-80, the Companion 

 gives the 2d Equation + 9h. 30m., and this gives the true time 20d. 3h., 

 38m. p. m., and adding 3h. for diff. of longitude, the time of new moon 



* The Almanac in Rushton's work gives a day earlier by some mistake, which 

 (or 12 hours) appears to run through every month of the year. 



