INSTEUCTIONS. 



PART I.— PHYSICAL OBSERVATIONS. 



I._ASTRONOMY. 



1. Astronomical Data. (Eclipses of the Sun and 

 Occultations.) By J. R. Hind, F.R.S. 



Eclipse of the Sun, 1876, March 25. 



In longitude 60° West and latitude 82°, this eclipse commences 

 March 25 at 4^ 12-1'" local mean time, 139° from the Sun's 

 north point towards the west, and ends at &" 8*". Magnitude of 

 eclipse, 0*67. 



For any position not far from the above, the longitude of which 

 is X (taken negatively) and geocentric latitude /, the Greenwich 

 time t, of commencement of the eclipse, may be found from the 

 following formulae : — 



Cos « = 1-11253- [0-19595]. sin Z+ [9*95510] .cos Z.cos(A. + 36° 19-40 

 t= ^^ S^ 50^ - [3 • 57030] . sin cy + [3 • 52333] . sin I 



- [3-76690] .cos / . cos (A- 150° 2-00, 



and applying the longitude expressed in time to t, thus found, 

 the local mean time of first contact is obtained. The quantities 

 within square brackets are logarithms. 



The distance of the point of contact on the Sun's limb from his 

 north point reckoning towards the west= 0)4-29° 45'. 



Eclipse of the Sun, 1877, August 8. 



In longitude 60° West, and latitude 82°, this eclipse commences 

 August 8 at 12'* 17*3™ local mean time, 16° from the Sun's 

 north point towards the west, and ends at IS** 21'". Magni- 

 tude of eclipse, 0-21. 



For any position not far from the above, the Greenwich time t 

 of commencement will be found from the formulae : — 



Cos cw = 2'52151- [0-22120] sinZ+ [9-93713] .cos /.cos (A + 289° 47-10 

 < = 17h22"» 57^- [3-49064] sin co- [3-30948] sin Z 



- [3-73517] .cos /.cos (A -26° 24-90. 



The distance of the point of contact on the Sun's limb from 

 his north point reckoning towards the west = w — 21° 36'. 



Note. — The north point is here to be distinguished from the 

 Sun's upper point or vertex. 



As an example of the application of the above formulae of 

 reduction of time of commencement, the calculation may be made 

 for the position assumed in the original calculation upon which 

 the equations are founded, viz., longitude 60° or 4'' West, and 

 latitude (geographical) 82°. To reduce the geographical to the 

 geocentric latitude (/), a correction is to be applied which may 

 be taken from the Table at p. 57 of " Appendices to various 

 " Nautical Almanacs between the years 1834 and 1854 ; " with 

 argument • 82°, this correction is 3-1' to be subtracted from the 

 geographical latitude, and hence /=81° 56*9'. 



