itions of the Earth and
Mars at the various Oppositions of Mars, from 1892 to 1924._

_Past Oppositions are shewn by the firm lines with the dates outside the
Orbit of Mars. Coming Oppositions are indicated by the dotted lines with
the dates inside the Orbit._

_The distance between any two consecutive Oppositions represents the
distance in excess of one complete revolution in its orbit passed over
by the planet since the last preceding Opposition. These distances are
greater on the left hand side because of the planet then being nearer
the Sun and consequently travelling more rapidly._

_Drawn by M. Wicks._

Plate VI]

Resuming the conversation, and keeping as calm as I could in the
circumstances, I placed the matter before him in all its aspects, and
after we had been talking together for a long time, he seemed to be able
to take a more reasonable view of the position. In order that something
might be done to keep his mind from dwelling upon his proposal to return
to England, I suggested that we should go to the store-room and
thoroughly overhaul it.

He agreed to this, accompanying me to the store-room and pointing out
the different places he had searched. The tins were in several sizes,
but all were made square in order that not an inch of the available
space might be wasted. We looked into a large number of tins which had
not previously been examined, but without finding what we wanted.

At last a thought occurred to me, and I said: "You tell me, John, that
you are quite certain you put up the tobacco and labelled the tin
yourself, yet the tin so labelled was found to contain tapioca! Do you
remember where the tapioca was stowed away?"

He pondered awhile, with his chin resting upon his fingers, then
suddenly replied, "Yes, I think I know where it is," and, taking me over
to another cupboard at the far end of the room, we made a further search
and at last found the tapioca tin, opened it, and lo, there was the
missing tobacco!

"Well, I'm blest!" said John, very slowly drawing out the words; then
all his ill-humour suddenly vanished, and he burst into a most hearty
laugh, in which I joined. Our laughter, indeed, was so mutually
contagious, and so often renewed, that we had to sit down to finish it
and recover ourselves.

Then John remarked, "Now, Professor, I think I can explain it all. You
see I prepared and labelled those confounded tins before loading them
up; so I suppose that when stowing away the