October 14, 1921] 



SCIENCE 



357 



SIDEWALK MIRAGES 



To THE Editor of Science: A number of 

 communications, published in Science during 

 tbe past year, on " Sidewalk mirages " having 

 recently come to my attention, I would like 

 to add my experience with this phenomenon to 

 those which have been related. I have driven 

 over a stretch of road, part asphalt and part 

 concrete, daily for the past two years, and 

 have looked for mirages under every condi- 

 tion of the weather. Over the distance of 

 the three miles of roadway I have marked 

 every spot where the mirage occurs. 



The nature of the road surface seems im- 

 material, but the effect of a " water surface " 

 can be obtained wherever the level of the 

 eye approaches that of the road surface. The 

 mirage is not visible in cold winter weather 

 and it is best during the very hot days in July 

 and August. I believe that the intensity of 

 the effect is unquestionably a function of the 

 temperature of the road surface and the air 

 immediately above it. That one observes a 

 true mirage in this phenomenon and not a 

 simple reflection can be demonstrated by the 

 fact that an object " mirrored " on one of these 

 surfaces will show an angle of incidence of 

 probably 45° or greater, whereas the angle 

 of reflection is, as stated previously by another 

 observer, very small, approximating a few de- 

 grees only. 



Mirror-like effects on asphalt roads are com- 

 mon, but have not the clarity of the images 

 seen in a mirage, nor can mirror effects, due 

 to reflection simply, be seen on a concrete road, 

 so far as I have observed. 



The position of the sun is of no influence, 

 as mirages have been observed at the same 

 spot at all times of the day. 



Allan F. Odell 



Cabnet's Point, N. J. 



DISCOVERY OF A PREHISTORIC ENGRAVING 

 REPRESENTING A MASTODON 



To THE Editor op Science: It may be of 

 interest to you to learn of the recent reex- 

 amination of Jacobs' Cavern, a prehistoric 

 rock-shelter located in extreme southwest 

 Missouri, some three miles from Pineville, 

 county seat of McDonald County. This 



cavern was examined by Dr. Charles Peabody 

 and Mr. Warren K. Moorehead, of Phillips 

 Academy, in 1903, report of their examina- 

 tion appearing in 1904 in Bulletin No. 1, 

 " Exploration of Jacobs' Cavern." 



Subsequent periodical and amateur investi- 

 gations carried on by the writer, who now 

 owns the land upon which this cavern is 

 located, have resulted in the discovery of a 

 number of very interesting artifacts. Chief 

 among these are bone and horn awls, flint 

 implements, engraved and polished imple- 

 ments of stone, and shaft straighteners and 

 smoothers. Portions of an adult human skele- 

 ton, accompanied by an engraved sandstone 

 pipe, have also been found. 



The latest discovery was made on April 17, 

 1921, when the writer and Mr. Vance Ran- 

 dolph exhumed several engraved, perforated, 

 and otherwise ornamented bones. These were 

 apparently firm and sound but as a precaution- 

 ary measure pen drawings were made im- 

 mediately. Nevertheless, upon being examin- 

 ed a few weeks later, it was found that the 

 bones were rapidly disintegrating. Immediate 

 preservative treatment was resorted to but 

 was so limited by local conditions that it was 

 found impossible to save more than the most 

 important specimen. 



In many respects this bone is very inter- 

 esting. One side bears an engraving which 

 prominent archaeologists have agreed seems to 

 resemble a mammoth or mastodon. The re- 

 verse side bears two rows of parallel zigzag 

 lines, lengthwise of the bone, the design cor- 

 responding closely with those found on the 

 sandstone pipe. This design is also ac- 

 companied by another evidently intended to 

 represent some member of the deer family. 



The writer felt that Phillips Academy was 

 naturally entitled to priority rights of reex- 

 amination of the cavern. However, Mr. 

 Moorehead found it impossible to visit the 

 cavern and recommended that Dr. Clark Wiss- 

 ler, of the American Museum of Natural 

 History, make the examination. Dr. Wissler 

 is now on the ground for that purpose. 



Photographs of the most important speci- 

 mens are in process of preparation and a 



