there had been just a single instant like II, which they could note accurately. Then they would have found out the Sun's distance very exactly. Unfortunately it was not so, and they knew from previous Transits that it would not be so. Instead of

an appearance like II, they knew they would see something like Fig. 16, the black disc being not at all round, but pear-shaped. This does not mean that Venus is really of that shape, for when it is fully on the Sun we can see that it is properly round, as in Fig. 17; and we also see that it has an atmosphere like ours, through which the Sun's rays are bent.