192 



SCIENCE. 



LN. S. Vol. XVI. No. 396. 



Jr.; 'The Red Sandstone of Diabolo Moun- 

 tains, Texas,' E. T. Dunible; 'Cretaceous and 

 Later Rocks of Presidio and Brewster Coun- 

 ties,' E. T. Dumble; 'A Preliminary Report 

 on the Austin Chalk Underlying Waco and 

 the Adjoining Territory,' illustrated with 

 half-tone engraving, John K. Prather; Pro- 

 ceedings of the Academy for 1901; List of 

 Patrons and Fellows; List of Members; Con- 

 stitution, in all covering 138 pages. 



FREDEftIC W. SiMONDS. 



Univeesity of Texas. 



DISCUSSION AND CORRESPONDENCE. 

 IRIDESCENT CLOUDS. 



To THE Editor of Science: The letter of 

 Mr. Ward in Science of July 4, concerning 

 iridescent clouds, leads me to record my obser- 

 vations of similar phenomena. From my own 

 observations, covering five years in Princeton, 

 Williamstown, Mass., and Baltimore, and 

 seven years in Boulder and Denver, Colo., I 

 am led to think that iridescent clouds are of 

 very much more frequent occurrence in Col- 

 orado than in the Eastern States. And they 

 occur much more frequently near the moun- 

 tains than at a short distance out on the plains. 



Boulder is situated immediately at the base 

 of the eastern foothills of the Rocky Moun- 

 tains, these foothills being from 1,200 to 3,000 

 feet higher than the plains, upon the edge, of 

 which the town is built. Just above these 

 foothills a stratus cloud sometimes forms, es- 

 pecially in winter, whose lower edge- is often 

 bordered with a band of color, frequently very 

 bright and clear. These colored bands occur 

 from ten to twenty minutes after sunset. The 

 cloud usually lies at a distance of 5° or 10° 

 above the horizon and is often almost abso- 

 lutely horizontal. The colors extend along the 

 lower edge for a distance of 15° to 30°, being 

 about 1° or 2° wide. 



At other times I have seen great patches of 

 cirrus clouds which were most beautifully ir- 

 idescent. One of these I saw at about eleven 

 o'clock which covered a space perhaf)s 5° or 

 more each way and which was about 15° or 

 20° east of the sun. It lasted for ten or fifteen 

 minutes, there being very little motion of the 

 clouds on that day. At other times I have 



seen many small patches of color, mostly 

 bluish-green and pink, appearing simultane- 

 ously in light cirrocumulus clouds. These 

 usually occur about the middle of the after- 

 noon. I have on a single occasion observed 

 a similar effect produced by the full moon. 



Denver is situated about twenty miles from 

 the foothills. Although I have not kept a 

 record, my observations during the last two 

 years convince me that these cloud colors 

 are seen much less frequently here than in 

 Boulder. 



I wish also to speak of a related phenomenon 

 of very much less frequent occurrence. On 

 July 5, I was looking toward a nimbus cloud 

 from which the rain was apparently falling 

 beyond a mesa which lies about five miles 

 east of Boulder. It was between four and five 

 o'clock in the afternoon. There appeared in 

 the cloud a patch of rainbow colors about 10° 

 long by half as wide. The colors were in the 

 order of the rainbow, but the bands were very 

 much broader and qiiite irregular. The colors 

 lasted for ten or fifteen minutes. The posi- 

 tion of the sun precluded the possibility of the 

 colors being produced in the same way as in 

 an ordinary rainbow. 



I have but once before observed the same 

 phenomenon. In the spring of 1895, I was 

 teaching in Grand Junction, which is situated 

 in the valley of the Grand River in the western 

 part of the state. To the east of the town 

 at a distance of about thirty miles the Grand 

 Mesa rises to a height of 5,000 or 6,000 feet 

 above the valley. On May 1, I observed a 

 nimbus cloiid, from which rain could be seen 

 falling, lying in the eastern end of the valley 

 and so low that the top of Grand Mesa could 

 be seen above it. About half past three I saw 

 in this cloud a strip of color extending north 

 and south about 10° and about 5° wide. The 

 red was above and about 10° or 12° from the 

 earth. (These data are copied from my diary 

 of that date.) The colors were quite as bright 

 as in a brilliant rainbow and included all the 

 colors of the rainbow. As in the former case, 

 the position of the sun made it impossible to 

 explain the production of the colors on the 

 basis of the theory of the rainbow. 



High School. Denver. E. Waite Elder. 



