JOURNAL AND PROCEEDINGS. 127 
was the first occurrence on which the phenomenon was ever actually 
witnessed, and then only by himself and a friend named Crabtree. 
Horrocks was a clergyman and had made calculation, and watched 
with great care, assisted with very poor instruments, and nothing of 
the data to guide him that we have at the present day. Add to this 
the fact that the transit was timed to occur on Sunday, when he 
had other important duties to perform, we can imagine, and only 
our President fully understands the perturbation of mind of this 
young enthusiast, divided between the delivery of a sermon and the 
expectation of seeing such an important sight as the first known 
transit of Venus, His name is handed down to us through his 
fidelity to science and as an astronomer. But for this fact his name 
would likely have been forgotten. Is it too much to say that his 
zeal in the cause of science carries with it an assurance of his faith- 
fulness in his profession as a clergyman? Those of us who desire 
to learn how the transit of Venus will tell the distance from the Sun 
must prepare to encounter a geometrical problem of no little com- 
plexity. But we will try and explain the conception which is known 
to astronomers by the name of parallax, for it is by parallax that the 
distance of the Sun, or indeed any other celestial body must be 
determined. A simple illustration will enable us to understand. 
If we hold a pencil in front of us and look at a background, close 
one eye and note the position of the penci} on the screen or back- 
ground, then close that eye and open the other eye, we will notice a 
difference in the position of the pencil on the background. Now 
our friends at the back of this room will see a different displace- 
ment to those nearest the front of the room, and so we can thus 
associate with each particular distance a corresponding particular 
displacement. Thus we have the means of calculating the distance 
from the observer to the screen. It is this principle applied on a 
gigantic scale which enables us to measure the distance of the 
heavenly bodies. Let Venus correspond to the pencil, let the Sun 
correspond to the object on the screen. Instead of the two eyes of 
the observer, we place two observatories in two distant parts of the 
earth ; we measure the displacement of the observers and from that 
calculate the distance of the planet. All depends then upon the 
means we have of measuring the displacement as seen from the 
two stations, and the scale of the solar system is known. It was to 
