LECTURES. 43 
The idea sounds absurd, but the lady who left the following will 
is not of that opinion :— 
“‘T bequeath a prize of 100,000 francs to the Institution of France 
for the person, no matter of what nationality, who shall discover, 
within ro years from the present time, a means of communicating with 
a star, planet, or otherwise and of receiving areply. ‘ I have especially 
in view the planet Mars.’ ” 
One way to set about the communication is this. 
In some vast open plain we must draw the figure of Euclid’s Prop. 
47, Book I., so big that the Martians could see it. If they saw it they 
would at once recognise the presence of intelligent beings on the 
earth, and would reply in some similar way, perhaps by a figure of a 
better proof of the same important proposition. Of course there is no 
Euclid on Mars, but there must be right angled triangles. Every 
house builder consciously or unconsciously uses this proposition. If 
they build houses on Mars they must use it too. 
It is a glorious scheme in theory. The difficulties are these : 
Firstly as to the size of such a figure. The sides must be at least 
60 miles thick—hardly length z¢¢hout breadth—and thousands of 
miles long. Our blackboard must be as big as Europe. If we could — 
find a piece of level ground big enough who would pay for such an 
enormous work? Even if we made it the Martians could not see it for 
our skies are nearly always cloudy, and what is absolutely fatal, at the 
time when we see him best we appear to him but as the new moon 
does to us. 
It is hopeless; the lady’s 100,c00 francs will remain for ever 
unclaimed. Mars may be able to speak to us, but we shall probably 
never be able to reply. 
