260 Joty—On the Origin of the Canals of Mars. 
Effects of the motion of the Satellite through an atmosphere as a cause of the lines. 
It is remarkable that the presence of a satellite moving at such a distance 
from the surface of Mars as to be within Mars’ atmosphere affords an entirely 
different mode of explaining the formation of the double canals, or even triple 
canals, supposing certain other not improbable conditions to obtain: an explana- 
tion depending upon the atmospheric disturbance set up by the motion of the 
satellite through the atmosphere, and the effect of this on loose surface material. 
The photographic record of the compressional air-wave streaming back from 
a bullet advancing through the air at a velocity of a thousand feet per second, or 
more, is now familiar to everyone. The mechanical effects of such an atmospheric 
wave may be studied by directing the bullet over a surface of loose powder. 
Suppose, for instance, the bullet is fired close down over lycopodium or lime 
loosely dusted upon a plate of glass. It is found that the wind-track of the 
bullet consists of parallel mounds of powder which have been blown to either 
side from the central line. In many cases a central ridge is also raised to mark 
the passage of the bullet. The double or triple lines so formed present a 
remarkable uniformity of width and parallelism. In one of the experiments 
the bullet was a small pistol bullet, the velocity of which when passing over 
the powder was about 750 feet per second. ‘The bullet passed at a height above 
the powder which, estimated by perforations left in cardboard sheets erected at 
opposite ends of the plate, was equal to a little more than its own radius, clear 
of the surface of the powder. The two elevated ridges resulting from the passage 
of the bullet through the air overlaying the powder were separated by a clearance 
having a width of two-and-a-half times the diameter of the bullet. 
What the effects would be, even in a less dense atmosphere, if the bullet 
were magnified up to, say, fifty miles in diameter, and its speed increased to 
perhaps 20,000 feet per second, may well be imagined. Any loose material 
would doubtless be torn up and projected from the path of the satellite. The sand 
of an ancient ocean, or the disintegrated material due to weathering would be 
cleared off and banked-up in ridges not less than 150 miles apart. 
The manner in which double canals are observed to cross each other, the 
lines of one being carried right across the central space of the other, might 
suggest a difficulty in the way of this mode of origin. But if it be considered 
that long intervals of time must have separated the formation of these canals, as 
will be seen later, during which disintegration from various causes would lead to 
the accumulation of débris upon the plains, and the consolidation of the accumula- 
tions of past disturbances, the appearance observed is no serious obstacle to. this 
action being accountable, or in part accountable, for the canals. 
