g4: MISCELLANEOUS NOTES. 



tains. The cbillod air is not able to contain the same quantity of aqueous vapor, and part of it becomes 

 visible as foo- or snow. From June 18 to 22, 1857, I was delayed at the Eancho Tlamacas on the foot of 

 the Popocatepetl, at an elevation of 12,800 feet, for three days, the fog being so dense that we could 

 scarcely see at twenty yards distance; an image of the camp-fire, at night time, being reflected from it. 

 It snowed continually, while the thermometer during the day was about two degrees F. above, and at 

 night as much below the freezing point. 



During the dry season, from October till May, the atmosphere of the high-lands is always clear, except 

 when northerly winds blow; but generally about nine or ten o'clock in the mornings, mist begins to form 

 around the highest mountain peaks and accumulates rapidly, so that at eleven o'clock those parts of the 

 mountains, which are elevated more than 13,000 feet, are entirely wrapped in clouds. Small floating 

 clouds, which form sometimes in the vicinity, in calm weather generally unite with the larger masses which 

 envelope the peaks. In the afternoon these clouds sink lower down, and the upper snow-covered part 

 becomes visible again above them a short time before sunset. At this time they appear most beautiful, 

 tinged with a rosy, or sometimes of a reddish golden color, but immediately after sunset these brilliant tints 

 change into a dull lead color (bluish gray), and the clouds entirely disperse about this time, only occa- 

 sionally a light mist being noted in the valleys and on the meadows during the evening. There are, how- 

 ever, "times, particularly in January and February, when not a cloud is seen near the mountains for two or 

 three days in succession. 



The cumulus-clouds never extend much above the highest mountain-peaks, and their greatest height pro- 

 bably does not exceed 20,000 English feet. At greater elevations cirrus-clouds only are observed, which 

 appear here of a purer white color than when they are seen from the low-lands. This lighter appearance 

 is probably caused in a great measure by their contrast with the sky, which is here of a darker blue than 

 near the level of the sea. I had no means of estimating accurately the height of the cirrus-clouds, but 

 from their size and appearance, which do not diSer sensibly from that which they exhibit near the level 

 of the sea, as also from their slow motion, it would appear that they were at least from three to five miles 

 above the station of observation, or from six to eight miles above the level of the sea. 



A sensible efiect of the rarefaction of the air on the duration of the twilight is also observed ; twenty 

 minutes after sunset, stars of the fifth magnitude become visible, and fifteen minutes later the last traces 

 of twilight disappear on the western horizon. If the air is calm the stars appear in a quiet, planetary 

 light, and lose very little of their brightness as they approach the horizon. Stars of the sixth magnitude 

 may be still distinguished at an altitude of five degrees. 



I have never observed any striking electrical phenomena in heights above 13,000 feet, and during my 

 stay on the high plateau of Mexico, thunder and lightning occurred very rarely. On the plains it rained, 

 during the rainy season, on an average, not more than every third day, and generally only in the afternoon 

 from three to five o'clock, but at this time the fall was occasionally very heavy. The two last seasons 

 (1857 and 1858) were, however, considered by the natives as unusually dry. In the higher mountain 

 ridges (from 10,000 to 13,000 feet elevation) a drizzling rain falls, sometimes for days in succession, 

 increasing generally in the afternoon. 



My observations on the limits of animal life are so restricted as to be of little value. 



Several classes of birds, among which I noted the raven, are found near the limits of vegetation 

 (13,200 feet), and great numbers of parrots were noted on the western slopes of the peak of Orizaba, at 

 more than 10,000 feet of altitude. Wolves ascend as high, or even higher, than the ravens ; and I have 

 seen deer 12,000 feet above the level of the sea. 



