372 



The Transit of Venus in 1874. 



[July, 



In Fig. 2 the actual nature of the earth's passage through the 

 cones is illustrated, as exactly as possible, to scale. In this figure 



the circles a 1 8 b and a 2 7 b represent the sections of the outer 

 and inner cones where they cross the earth's orbit. For convenience 

 we consider these circles to be at rest, and examine only the efiects 

 of the earth's relative motion, boa is parallel to the ecliptic. 

 As the earth is in reahty moving from right to left in a direction 

 parallel to b o a, and with a less rapid motion than that of the two 

 circles a b, a b, it is clear that the earth's relative motion is from 

 left to right. Also, as the circles are crossing a o b from south 

 towards north (for Venus is at an ascending node both in 1874 

 and 1882) it is clear that the earth has a relative motion from 

 north to south. The triple sets of lines marked with arrows show 

 the actual direction of the earth's relative motion (the small circles 

 representing the earth in various parts of her passage). Calculation 

 shows that this relative motion is such that a central transit would 

 occupy nearly eight hours. The triple lines are inclined to a o b at 

 about 9^ degrees ; and 14 degrees to the east and west line e w. 



The actual path of the earth across the circles in 1874 and 

 1882 is indicated by the lower and upper sets of triple lines, 

 respectively. 



In considering the circumstances of the transit of 1874, I 

 dismiss all consideration of the phenomena marked (i), (ii), (vii), 



