OCCULTATION OF VENUS BY MOON 
129 
From these elements, together with the position of the place 
of the observer and the declination of the planet, the Mean Time 
of immersion and emersion of the center of the planet, the angles 
which these points make with the north point and the duration 
of the occultation may be computed. 
OBSERVATIONS AND MEASUREMENTS 
1. A photograph was taken before immersion at time Ti (point 
I of fig. 3). 
2. Immersion was observed at time T2 (point E). 
3. A photograph was taken after emersion at time T4, times 
Ti, T2, T4 were recorded on the chronograph in Gr. M. T. (Gran- 
ville mean time). 
4. The two negatives were superimposed and a positive made 
of same size with the reproducing camera. 
5. Prints were made of this positive for measuring with a mm. 
scale to tenths of millimeters. These measurements were after- 
w’ards checked with the comparator of the observatory. 
Reductions of observations 
Ti was found to be 17^^ 35"^ 14.0^ (Gr. M. T.) 
T 4 was found to be 18 57 06.0 (Gr. M. T.) 
T 4 -T 1 was found to be 1 21 52.0 = 34.26 mm. 
From this was found 143.38= 1 mm. 
T 2 was found to be (directly observed immersion) 17^^ 53™ 45®0 
T 2 -T 1 was found to be (from measurement of print) 18 13.3 
T 2 was found to be (from measurement of print) 17 53 27.3 
T 4 -T 3 was found to be (from measurement of print) 7 52.9 
T 4 — Ti — [(T 2 — Ti) + [(T 4 — T 3 )] = duration of occultation .... 55 45.8 
T 4 — (T 4 — T 3 ) = T 3 (from measurement of print, emersion) 18 49 13.1 
Comparison with calculation 
Time of immersion 
Calculated. 
Observed: T 2 . . . 
From print : T 2 . . 
Time of emersion 
Calculated: T3. . 
From print T 3 . . . 
17^55™48^24 (Gr. M. T.) 
17 53 45.0 
17 53 27.3 
18 52 12.12 
18 49 13.1 
