A CATALOGUE OF OBSEUVATIONS OP LUMINOUS METEORS. 363 



(9), the resulting two equations have been employed for iiuding- x and i/. Tlieso 

 equations are — 



- 2' = 0-G9o9.r-0-238o//, 

 + 50'=0;3129.r+0-49.13)/, 



which give a-= + 26', y=-|-8-i'. As I had no reason to suspect any azimuthal 

 disturbance of the insti'ument between Nos. 62 and 70, the ii:ter-\-al between tl\eni 

 being not more than seventeen minutes, I have similarly employed the equations 

 (6), (7), (13), and (14) for finding .r and i/. The two resulting equations are — 



- 15' =0-o48ar - 0-3424?/, 

 -78'=00002.r-0-4755}/, 



which give .r= +70', »/= +105'. These values are not accordant with those ob- 

 tained from the other set of equations ; but perhaps the deviations from the mean 

 values, which do not exceed 25' in altitude and 40' in azimuth, are not greater than 

 what might be expected from the mode of observing and the character of the in- 

 strument. I have therefore adopted the values .f = .50', i/=l2o', using 50' instead 

 of the exact mean 51' for facility of calculation. I tried other combinations of the 

 equations, but found none that gave as probable results as those derived from the 

 above values of x and i/. 



Hence the values of n derived from, the equations (8) and (9) arc —52° 57' 

 and - 52° .30', the mean of which, —52° 44', is adopted for Nos. 1 to 17 of the series, 

 a note having been made that just after No. 17 the stand was disturbed. Tlie 

 values of n, similarly derived from the equations (10) to (14), are —5(3° 47', —oo° 

 33', -54° 27', -54° 20', and -54° 1'. The two first seem to indicate vmsteadiness 

 of the stand, but as their mean does not greatly differ from the mean of all, it was 

 thought right to adopt the latter mean, viz. —54° 37', for all the observations after 

 No. 17. 



When the same values of a; andy are substituted in the equations (1) to (7), the 

 resulting values of m are 19° 24', 19° 17', 18° 57', 19° 7', 18° 44', 17° 43', and 17° 43', 

 the mean of which is 18° 42'. For verification of this result I also obtained the 

 index-correction in the following manner : — An adjusted spirit-level was placed on 

 the upper flat side of the bar, find the bar being made to point horizontally by 

 bringing the bubble into middle position, the altitude-circle was read oft". The same 

 thing was done after changing the azimuth by 180^. The two readings being 71° 

 15' and 71° 35', the complement of half their sum is +18° 35', which consequently 

 is the index-correction. By another trial made in azimuths 90° from the former, 

 the two readings were 70° 0' and 73° 0', and the index-correction is consequently 

 +18° 30'. The mean between the two residts, viz. 18° 33', is the adopted value 

 of m ; this mode of determining it being thought to be more accm'ate than the otlier. 

 The small difference between this value and -1-18' 42' is considerable confirmation 

 of the accuracy of tlie adopted values of .r and y. It should be added that in ob- 

 taining these corrections, the meteoroscope was placed, as nearly as could be con- 

 jectured after about a month's interval, in the same position that it had during the 

 observations, and that consequently the values of x and y may be inferred from the 

 differences of the altitude-readings in the respective positions. The values thus 

 obtained are a-=-|-10', y=:+90'. As I could not be sure that the meteoroscope in 

 this trial had exactlj^ the same position as before, I have preferred using the values 

 of a: and y deduced from the observations of stars. 



Representing now by A and Z the azimuth- and zenith-distance readings for the 

 observation of any meteor, the following equations were employed for calculating 

 its true azimuth and altitude as given by the observation : — ■ 



)=71°12'-Z+50'cos(A+H) + 125'sin(A-l-rt)-re 

 = A+;i+ tan/3 (50' sin (A+k)+125' cos ('A+».))- 



True altitude (/3)=71° 12'-Z+50' cos (A+H) + 125'sin (A-l-rt)- refraction. 

 True azinmth 



The value of « is —52° 44' for Nos. 1 to 17, and —54° 37' for the remaining Nos. 

 The constant 71° 12' is 90°- 18° 33'- 15'; the correction -15'' being applied for 



