12 



FAUNA OF MAYFIELD'S CAVE. 



LIGHT. 



The partition at the entrance, although rather open, shuts out much 

 of the Hght from the first part of the cave and greatly increases the twi- 

 light, causing the stretch of the cave from the entrance to the first turn 

 to have a more uniform and diffused light than it would otherwise have. 



The two sharp turns in the course of the cave near the entrance, 

 one 50 feet in and the other 70 feet farther in, regulate the rays of light 

 from the outside in such a way as to produce a definite area where 

 there are direct rays from the outside and also a definite area where 

 there are only reflected rays directed inward from the wall at the first 

 bend. Beyond the second turn one's eye, even when directed toward 

 the dimly lighted portion, can not discern the faintest light. This 

 angular course of the cave produces fairly well defined areas of strong 

 twilight, dim twilight, and absolute darkness, the areas of course merging 

 into one another to some extent. 



TEMPERATURE. 



The average temperature of the cave in its remote parts is the mean 

 annual temperature of the region. The average of temperatures taken 

 at "42" is 11.52° C, but during the months of July and August no 

 temperatures were taken here. The average for the whole year at 

 "42" would doubtless run very near 11.9° C, the mean annual temper- 

 ature of Bloomington. 



Temperatures observed at Mayfield's Cave. 



[Temperatures are given :u degrees centigrade. The figures given at the heads of the columns 

 refer to points indicated by corresponding figures in plate 2.] 



»At mouth of cave. >>Passage oflf " 27," 11.4°. 



