Dr. Phillips on the Telescopic Appearance of the Planet Mars. 315 



from 20° to 30° north and south of that line. This may perhaps 

 be understood by the drawings selected for illustration, especially if 



Fig. 3. — The hemisphere of Mars, opposite to fig. 1 : seen October 15th and 16th. 

 With a specially dark hand. 



compared with an orthographic projection of the latitudes*. (Still 

 better by means of the globes which accompanied the communica- 

 tion, constructed by the author, one from his own sketches, the 

 other from those of Mr. Lockyer.) 



Allowing the white spaces to be land, which reflects light as the 

 moon in opposition, it seems a natural supposition that the shady 

 spaces should be called sea ; and this may be supported by the 

 obvious requirement of water somewhere on Mars, to agree with the 

 alternate gathering and melting of the snow round the poles. Still, 

 every observer remarks no small resemblance of some of these shady 

 tracts with particular parts of the unequally tinted grey surfaces of 

 the moon. A positive proof of ocean on the disk of Mars would be 

 afforded by the star-like image of the sun reflected from the quiet 

 surfacef, or the more diffused light thrown back from the waves; 



* The inclination of the axis of Mars to the observer was, on the 1st of October, 

 1862, 25^°, as Mr. Main has informed me. 



f The quiet image here alluded to would not exceed -^th of a second of angle 

 at the opposition, if no allowance be made for irradiation. But much allowance 

 must be made for this. A thermometer-bulb, with diameter half an inch, reflects 

 the sun as a star visible by the eye at 25 yards' distance, the reflecting surface in 

 this case being about 2io tn °f an i" cn * n diameter, and therefore (if no irradia- 

 tion were allowed for) the angle subtended at the eye would be only about J ", 

 By employing on Mars a power of 300, the -^-' becomes relatively magnified 

 to 15". 



The reflective power of water at a nearly vertical incidence is, however, so 



