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POPULAR SCIENCE MONTHLY. 



next reconnoitered the upper course of the 

 Maraiion River on the eastern slope of the 

 Cordillera in the Peruvian north, whence the 

 reports about the ruins of Kue-lap had 

 created great interest. He passed the his- 

 torically celebrated town of Cajamarca; 

 traversed in the department of Amazonas an 

 exceedingly broken and uneven country ; 

 and secured a complete plan of Kue-lap, with 

 a number of details, furnishing data to cor- 

 rect previous accounts and surveys. He also 

 gathered a number of traditions relative to 

 occurrences anterior even to the time when 

 the Incas began to make raids across the 

 Maranon. After exploring many other ruins, 

 the political conditions in Peru becoming un- 

 pleasant, Mr. Bandelier went into Bolivia, 

 where he spent some time on the island of 

 Titicaca, established the height of about 

 14,500 feet as the uppermost limit of seden- 

 tary occupancy in ancient times on the south- 

 ern side of Illimani, and examined the slopes, 

 up to 15,400 feet, of the great peak of Ka- 

 ka-a-ka, or Huayna Potosi. At last accounts 

 he was preparing for a journey to Pelechuco, 

 in the northwestern corner of Bolivia. 



Tcmperatnre Levels in Lake Mendota^ — 



Prof. E, A. Birge, of the University of Wis- 

 consin, has been pursuing studies of the 

 " Plankton " of Lake Mendota in that State, 

 with a prime view to making a contribution 

 to the natural history of an inland lake as 

 " a unit of environment." He finds that 

 during the summer the difference in tem- 

 perature between the surface and the bottom 

 may amount to 10^, 12', or even 15 C, but 

 the decline in temperature from surface to 

 bottom is not uniform as the depth decreases. 

 If a series of temperatures is taken about 

 the 1st of August it will be found that there 

 is a layer of surface water from about 

 twenty five to forty feet ia thickness, the 

 temperature of which is nearly uniform. 

 Immediately below this mass of warm water 

 lies a stratum in which the decline of tem- 

 perature is extremely rapid. This stratum 

 may be from about six to ten feet thick, with 

 a decline of nearly as many degrees centi- 

 grade per yard ; or it may be only about a 

 yard thick. This layer in which the tem- 

 perature decreases rapidly may be known as 

 the thermoeline — the Sprunsgchiet of German 

 authors. Below the thermoeline the tem- 



perature decreases toward the bottom at first 

 more rapidly and then more slowly as the 

 depth of water increases, but never showing 

 the sudden transitions which are character- 

 istic for the thermoeline. The thermoeline 

 was first noticed by Richter in 1891 in a 

 study of the Alpine lakes. Its origin was 

 attributed by him to the alternate action of 

 the sun warming the surface in the day, fol- 

 lowed by a cooling at night. The alterna- 

 tion of the conditions resulted in the forma- 

 tion of a layer of water of nearly uniform 

 temperature above the colder bottom water. 

 In Lake Mendota the concurrence of gentle 

 winds and hot weather is essential to the 

 formation of the thermoeline. The warmth 

 of the surface water, received from the sun, 

 is distributed through a certain depth of the 

 lake, a depth which is proportional to the 

 violence of the wind and the area of the lake. 

 In a lake of the size of Mendota the water 

 would be of uniform temperature from top 

 to bottom if it were always agitated by vio- 

 lent winds. On the other hand, if the weather 

 were perfectly calm, the lake would be 

 warmed only to the depth to which the rays 

 of the sun could directly penetrate. 



Cnrions Photographic Effects. — Since 

 the rise into prominence in 1895 of the X- 

 ray phenomena, there has been a greatly 

 increased interest among physicists in the 

 even more curious but apparently closely 

 allied phenomena of normal physical ema- 

 nations from certain surfaces which have 

 the property of influencing the sensitive 

 plate, and in some cases even impressing 

 an image on such insensitive substances as 

 glass, copper, etc. These phenomena have 

 been variously labeled scotography, vapog- 

 raphy, etc , but there has not as yet been 

 sufficient insight gained into their causes to 

 allow of a truly descriptive title. Dr. W. J. 

 Russell, who has made this phenomenon the 

 subject of his last two Bakerian lectures be- 

 fore the Royal Society, is authority for the 

 following statements. He had previously 

 found that zinc, other metals, wood, straw- 

 board, and printed papers, when placed in 

 contact with a dry plate, had a certain action 

 on it, which enabled it to be developed as if 

 it had been exposed to light. In his later 

 lecture he recounts a number of additional 

 experiments. Zinc and other materials, 



