J. LeConte — Phenomena of Binocular Vision. 97 



In July, four and a half months after the discharge, as Mr. 

 Yan Slyke reports, the emptied basin of Halema'uma'u contained 

 •within " a rising cone of loose rocks." The cone surrounded 

 the central part of the basin, and consequently a great and deep 

 trough-like depression several hundred feet wide separated it 

 from the walls ; it had a height in most parts of " perhaps 150 

 feet," and small cones and basins of lava existed at points in 

 the trough around it. 



Mr. Dodge's map and article (p. 99 of the preceding volume) 

 represents the rising cone as 930 and 1,100 feet in its diameters^ 

 and as having some points in its summit as high as the edge of 

 the basin — its condition in November, eight months after the 

 eruption. Still later, in January,* he represents the cone of 

 fallen blocks and lava debris as " perhaps 200 feet" above the 

 height in October, and speaks of the rising as going on " slowly, 

 as though floating on the surface of the new lava-lake." 



A "review of the phenomena, with conclusions" will com- 

 plete this account of the changes in Kilauea since 1823 ; and, 

 in the mean time, I hope to see the crater, in order better to 

 understand its present and past condition.. 



[To be continued.] 



Art. XII. — On some phenomena of Binocular Vision ; by 

 Joseph LeConte. 



No. XII. — Some peculiarities of the phantom images formed by 

 binocular combination of regular figures. \ 



[Read before the National Academy of Sciences at Washington, April 22, 1887.] 



The law of corresponding points is justly regarded as the 

 most fundamental law of binocular vision. Properly under- 

 stood it explains every phenomenon ; and no field of investiga- 

 tion can be more fascinating than to trace, on the one hand, 

 deductively the logical consequences of this law in resulting 

 phenomena, and on the other, inductively the phenomena back 

 to this law as their sufficient cause. The phenomena now 

 about to be described, and to be explained by this law, have 

 some of them not been heretofore described and none of them 

 satisfactorily explained. 



It is well known that the figures of a regularly figured plane, 

 such as a tessellated floor or a papered wall of regular pattern, 

 may be combined by crossing the eyes, or (if the figures be not 



* This Journal, xxxiii, 240, letter to the writer, dated Jan. 27, 1887. 



f For other papers on the same general subject see this Jour. 1868-1880. 



Am. Jour. Sci.— Third Series, Vol. XXXIV, No. 200.— August, 1887. 

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