1869.] The Transit of Venus in 1874. 375 



and no correction has been made for the equation of time. It 

 seems to me questionable whether the results are quite near enough 

 for practical purposes. They lie severally about 315, 920, 760, and 

 230 miles from the positions I have obtained for the corresponding 

 points. These corrections seem to me to appreciably affect the 

 question at issue. The following rough description of the situation 

 of the four spots referred to applies, however, almost as well to the 

 Astronomer Koyal's results as to mine : — ■ 



Most accelerated ingress takes place at a spot far to the north 

 of Owhyhee; most retarded ingress in a place far to the west of 

 Kerguelen's Land and Crozet Island. Most accelerated egress 

 takes place near the Antarctic continent in longitude far to the 

 east of Victoria Land; most retarded egress takes place in the 

 north-east of European Russia. 



The actual longitudes and latitudes of these places I have cal- 

 culated to be, in order : — 



Latitude. Longitude. 



(1) 39° 45' N 143° 23' W. 



(2) 44 27 S 26 27 E. 



(3) 64 47 S 114 37 W. 



(4) 62 5 N 48 22 E. 



We come now to considerations which requhe to be closely 

 attended to, as they involve the gist of the whole matter. 



If stations (1) and (4) were identical, it is clear that an observer 

 there, seeing most accelerated ingress and most retarded egress, 

 would observe the absolute maximum duration of transit. So if 

 the stations (2) and (3) were identical, an observer there would see 

 most retarded ingress and most accelerated egress, and so observe 

 the absolute minimum duration of transit. Or even if observers at 

 stations (1) and (4) could be brought into communication by means 

 of the telegraph,* as also those at (2) and (3), it would be possible 

 to render available the total difference of twice 25 m. 6 s., which 

 actually marks the dm-ations of transit in 1874 considered with 

 reference to the whole earth. This difference of 50 m. 12 s. would 

 exceed more than twofold the observed difference in 1769. 



But under the actual circumstances what has to be done is to 

 secure a station as near as possible to both the stations (1) and (4), 

 and so situated that the sun shall be fairly raised above the horizon 

 at the epoch of the internal contacts both at ingress and egress ; 

 and the like for stations (2) and (3). The examination of Figs. 

 1 and 2 (Plate) will show that there is a difficulty in fulfilhug each 

 set of conditions. The point marked " accelerated ingress " is far 



* Nothing but the consideration of expense renders this impossible or even 

 diiScult. 



