PRESIDENTIAL ADDRESS. 19 
Even with the largest telescopes yet made, these markings 
are not so clearly defined as to cause the acceptance of 
them as positive. The Savilian professor of astronomy at 
Oxford, Herbert Hall Turner, F.R.S., has the following 
remarks on this subject :-— 
“We have heard a good deal of late years of the canals of 
Mars, and there is no doubt at all that certain straight markings 
on the planet’s surface have been detected. Many of us have 
sufficient faith in that wonderful observer Schiaparelli to believe 
that these are occasionally seen double. But as regards the 
interpretation of such markings—the notion that because they are 
called canals it is implied that there are inhabitants on Mars, 
who have dug them for irrigation purposes—we must exercise 
more caution. To realize the value of our information, consider 
first how much further away Mars is than the moon—about 200 
times at least, and generally much more. Now 200 is the 
magnifying power of a good telescope, that is to say, the 
magnifying power which can be used with advantage. It follows 
then, that whatever a fair telescope enables us to see on Mars 
could be seen on the moon with the naked eye; and it may be 
added that whatever the largest telescope in existence would 
enable us to see on Mars could be seen on the moon with a 
pocket opera-glass, for our gain from the recent increase in size 
of telescopes is well within that represented by a small opera-glass 
as compared with the eye. Hence, let any one look at the moon 
with the naked eye, or even with a small opera-glass for traces of 
canals or other signs of life of any kind, and he will begin to 
understand the caution which must be exercised in drawing 
conclusions, however attractive, as to the habitability of the 
planet. We want, in fact, an increase of our optical resources by 
a thousand times at least to get any satisfactory intelligence of 
this kind, whereas the advances of the last century would be 
represented by a factor not greater than 10, and there seems no 
chance at present of our getting to 100; we might manage 20, 
perhaps, by slow and costly advances, but 100 seems impossible. 
