. The transit of Venus. distinct observations made at each station, theinternal contact at ingress and the internal contact ategress. The time of an internal contact is the timeat which Venus appears to be just wholly within thesuns disc. These two times must be accuratelydetermined ; they will be separated by an interval ofnearly four hours. Fig. 12 represents the illuminatedhemispheres of the globe at the time of ingress andat the time of egress respectively in 1S74. At eitherof these epochs the sun will be visible from everyplace marked on the corresponding map. The sunwill be vertical at t
. The transit of Venus. distinct observations made at each station, theinternal contact at ingress and the internal contact ategress. The time of an internal contact is the timeat which Venus appears to be just wholly within thesuns disc. These two times must be accuratelydetermined ; they will be separated by an interval ofnearly four hours. Fig. 12 represents the illuminatedhemispheres of the globe at the time of ingress andat the time of egress respectively in 1S74. At eitherof these epochs the sun will be visible from everyplace marked on the corresponding map. The sunwill be vertical at the place occupying the centre ofthe map ; at all stations near the edges of the map So THE TRANSIT OF VENUS. [chap. the sun will at that time be near the horizon. Thepoint from which the phenomenon will be firstobserved is there indicated, and likewise the point atwhich it is last seen. Straight lines are drawn acrosseach map, and the hours marked upon them indicatethe time at which the phenomenon will be seen. \AAAN \. Figs. 13. 14. taken from a paper by the AstronomerRoyal in the Monthly Notices, show the same factsfor the transit of 1882. Take now the case of two particular stations. Atsome point on the east coast of China the ingress isaccelerated by 6 minutes, but at the same point the III.] THE TRANSIT OE VENUS. 39 egress is retarded 7 minutes ; consequently the dila-tion of the transit is lengthened 13 minutes. Again,at Kerguelens Island the ingress is retarded 10minutes, while the egress is accelerated 5 then the duration of the transit is shortened 15minutes. The difference in duration as observed
Size: 1594px × 1568px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1870, bookidtransitofven, bookyear1874
