242 KANSAS CITY REVIEW OF SCIENCE. 



with enthusiasm. The relative distances of the planets from the Sun and from 

 each other, are found by measuring the angles described in a specified time by 

 the exteripr planets at times of opposition, and those of interior, by the angles 

 presented at elongations. For two centuries it has been known that if we call 

 the distance from the earth to the Sun i that of Venus is .723 ; then the distance 

 of Venus from the earth is of course .277. Now in the diagram the wall is the 

 Sun, V Venus, C an observatory on one side of the earth and D another on the 

 opposite, near as can be. And it is endeavored to have C and D at the extrem- 

 ities of a diameter of the earth that is perpendicular to the plane of the ecliptic. 

 As the latitude and longitude of C and D are known, the arc of the great circle 

 a circumference of the earth passing through them being interrupted thereby, is 

 known. Having the arc we know its chord in miles, which is none other than 

 the straight line through the earth, joining each station. The first step of each 

 party on arriving at their destination is to find their precipe latitude by direct obser- 

 vation on fixed stars. Then the longitude is determined by chronometers in con- 

 junction with transits of fundamental stais. At length the eventful moment ar- 

 rives, the instruments are all in adjustment, and Venus, a black ball, just cuts off" 

 a ray of Hght from the eastern limb of the Sun. The absolute instant of contact 

 in Greenwich time is noted and recorded, the exact point of ingress on the solar 

 edge measured from the north point is also recorded and the transit progresses. 

 This same observation is made from all the stations, accurate results being saved 

 at each for reference. 



The prepise time of disappearance of Venus from the western limb is also 

 noted, as well as the exact point of departure. Upon reaching home the 

 results are compared. Those observers who were stationed south of the earth's 

 equator will all bring in reports saying that they saw Venus make ingress and 

 egress at points further north on the solar disc than did those remaining at obser- 

 vatories in north latitude. 



Thus — if an astronomer at Washington compares notes with the one who 

 went to Santiago, he will find that the southern observer has record of contacts 

 at points farther toward the north point of the Sun than he has. Since these 

 places of contact are accurately measured, the distance asunder of the chords A 

 and B becomes known in seconds of arc. Venus appears to all observers wheth- 

 er north or south of the equator, to traverse straight lines from east to west across 

 the Sun, but these lines are chords of arcs whose sines are found in any table. 

 But the space between the chords corresponds to a known difference in position 

 of observers on the earth, depending directly on the length of the straight line 

 through the earth connecting any two observing stations. Then : 



.277 : .723 : : i : 2.61. 



That is, the ratio of the distance of Venus from the earth is to its distance 

 from the Sun as t to 2.61. Hence the space between the chords on the Sun is 

 to space between two stations on the earth in the same ratio or as 2.61 is to i. 

 In other words the distance apart of the chords is 2.61 times greater than the 



