JOURNAL AND PROCEEDINGS. 125 
its cloud, and we can imagine the difficulty that astronomers have 
in dealing with it, but by observing it in daylight, to avoid the glare, 
and not waiting till the crescent becomes too thin by choosing the 
quadratures and making use of great atmospherical purity such as 
we find in Italy, observers succeed from time to time in perceiv- 
ing greyish spots which may indicate the place of its seas. 
This paper would be wanting in completeness without some 
reference to what is known as the transit of Venus. This cannot 
be described as a very attractive sight, or a spectacle challenging the 
attention of ordinary people, because it has taken place for thousands 
of years without astronomers even suspecting it. It is not a sight 
such as a comet, for instance, nor even as an ordinary shooting star, 
yet scientifically of the greatest importance, because it helps enquir- 
ing minds to solve one of the greatest problems that has ever 
engaged the mind of man. By the transit of Venus, astronomers 
determine the scale upon which the solar system is constructed. We 
have mentioned before, in the early part of the evening, the bodies 
composing our solar system. We may know the relative distance of 
the planets from the Sun, their size, etc. Difficulty arises as to the 
actual size of the system, as well as the shape. Flammarion says 
we may draw a map of Europe or America, outline its continent with 
rivers and mountains, or we may get an architect to draw the plan 
of a building ; we may see the position of the doors and windows, 
the shape of the roof and the position of the chimneys, but we know 
nothing of its size without a scale, showing us how much the scale is 
to the foot. Having the scale, the plan is intelligible and conveys 
to our mind the exact idea of the extent and proportion of the 
building. So astronomers need a scale to tell how many millions of 
miles on the heavens correspond to an inch of scale on the map. It 
is at this point that great difficulty has been encountered, and while 
there are several ways of settling the difficult problem, one of the 
best is that presented by the transit of Venus across the Sun’s disc. 
Herein lies the importance of this rare event—rare because that 
while the transits of Venus occur in pairs of eight years between each 
transit, yet, after a pair of transits, one hundred years elapse before 
another transit, followed by another in eight years. A transit took 
place in 1761 and again in 1769 ; in 1874 and 1882. Then a long 
period, for another transit will not occur until 2004, followed by 
