1901.] LOWELL— SUPPOSED SIGNALS FROM MARS. 171 



to longitude centre 41 °, without revealing any irregularity. The 

 phase loss was then 27 , as against 36 in December. So that nine 

 degrees should be deducted from these figures to make them com- 

 parable. It thus appears that on this date both projections should 

 have been visible, one after the other, had they still existed. Neither 

 was seen. Nor was any projection seen at any other time during 

 the opposition. Permanences like mountains, therefore, could not 

 have caused them without doing violence to the observations. 



From the impermanency of place of the projections it is clear 

 that they could not have been fixed to the planet's surface — that is, 

 they could not have been mountains. We are left, therefore, with 

 the alternative that they were a something floating in the planet's 

 air capable of reflecting light, or in other words clouds. Secondly, 

 from the similarity of their appearances, we infer that they were 

 the same clouds which had shifted their position during the twenty- 

 four hours that elapsed between their apparitions. They may, of 

 course, have been wholly distinct condensations of vapor which 

 happened to agree in behavior. The probability of this we shall 

 now investigate by considering the phenomena more in detail. 



13. It is necessary to begin by determining their height, for it 

 will be found that this height enters as a function into the equations 

 of position. If we call 



d— the perpendicular distance of the tip of the projection from 

 the terminator ; 



P — P. A. = <p = angle between the tangent to the terminator and 

 the axis of rotation ; 



E = the angle of the phase ; 



A = the phase latitude, that is the latitude reckoned from the 

 phase equator ; 



a = the radius of the disk in seconds of arc ; 



a = the radius of the planet in miles ; 



#:=the angle subtended at the centre of the disk between the 

 tip of the projection and the point on the terminator at the same 

 phase latitude, 

 we shall have 



d 



tan x = - 



cos 6 sin M. a. cos A 



and h = height will be 



h = sec x — 1. a cos 2 A 



Performing the numerical operations, we find for the height on 



December 7, 



h = 1 3.4 miles. 



