478 Transactions. — Miscellaneous. 



the Earth's surface projected to a plane passing through that 

 centre. The data for the forthcoming occultation of $ re- 

 quired are the following : — 



1. The equatorial horizontal parallax, corrected for the 

 latitude of the place and diminished by that of ? (P.) 



2. The geocentric latitude of the station (l). 

 . 3. The declination of ? (8). 



4. The difference of 8 of ? and j) (A). 



5. Time of d in E.A. 



6. Hour angle of $ at that time. 



7. Moon's semi-diameter (/x). 



8. Moon's hourly motion E. 



9. Moon's hourly motion S. 



Unless great accuracy be required, the corrections for 

 parallax and latitude need not be made, but the figures taken 

 as they are given in the " Nautical Almanac." They will be 

 sufficient to tell us when to watch for the phenomena. The 

 corrections being made, great accuracy can be obtained. 



P. The corrections for parallax have been calculated for all 

 latitudes, and may be found in books of nautical tables. It is 

 0" at the equator, and increases towards the poles, wdiere it 

 amounts to 12", or i- of a minute of arc. In the present case 

 P. is 56'; the correction is 5", to which we add that of 5 =7", 

 making together 12" to be subtracted: 56' -12" = 55' 48" = 

 55'76'. Take then from the diagonal scale in the compasses 

 55-8 for Earth's radius, and describe a semicircle, to repre- 

 sent the S. half of Earth's disc. The centre ® represents 

 Earth's centre. Erom erect a perpendicular, which is the 

 axis of projection, through which passes the plane of projec- 

 tion (at present perpendicular to the paper). The planet's 

 declination (8) is 9° 57' S. We suppose ourselves in the plane 

 of the paper towards the left hand. Our declination being 

 S., the S. pole of the Earth must be turned towards us by 

 the amount of our 8. Mark off the arc of 9° 57' (10°) 

 towards the left of axis of projection, through this draw the 

 axis of Earth. We next waiit the parallel of Wellington. 

 Its latitude is =41° 17' S., its co-latitude 48° 43'. Adding 6' 

 for correction, we have 48° 49' (say, 50°) which set off from 

 tbe polar axis in the same direction and mark the point I. 

 Set off the same (50°) to the right of polar axis, mark it l^, 

 and through these points draw the parallel of latitude, whose 

 centre is on the polar axis. 



Now, looking from the left, we see these three points 

 Z, c, and l^ projected on the axis of projection. We have, 

 however, only to do with two of them, I and c, I being our 

 place when 2 is in transit, and c our place at her 6-hour angle. 



We next imagine the whole diagram turned a quarter 

 round, so that from being at the left in plane of the paper 



