. American journal of physiology. 930^1, the numberbeing the distance of the image Ij from the geometrical centre of thecornea, while the other images would be displaced by amounts pro-portional to the ratios of magnification given above. We should thushave the following values for the ordinates of the three images: 7i = 01,y-i - </)i,yz = — ^i- --Errors of Eccentricity in the Human Eye. 507 To an observing eye at a great distance in the direction 0.,, theprojection of a point midway between the images Ij and I3 on a planeperpendicular to the axis and close to both of th
. American journal of physiology. 930^1, the numberbeing the distance of the image Ij from the geometrical centre of thecornea, while the other images would be displaced by amounts pro-portional to the ratios of magnification given above. We should thushave the following values for the ordinates of the three images: 7i = 01,y-i - </)i,yz = — ^i- --Errors of Eccentricity in the Human Eye. 507 To an observing eye at a great distance in the direction 0.,, theprojection of a point midway between the images Ij and I3 on a planeperpendicular to the axis and close to both of them would be at\ (7i + J3) = Similarly, the projection of Ig on the sameplane would be at + that is, at ^ + The conditions of Helmholtzs observations were, first, that theangular distance between the source and the observing eye wasconstant, that is, that 0^ — 02= ±2\/r, the upper sign holding for thefirst position of the source and observer and the lower for the inter-changed Figure 2. The second condition was that the projections of the two pointsdefined above fell together in both positions of the source andobserver. These two conditions may be formally stated as follows: Source on temporal sideSource on nasal side 01 = ij/ — Si[/, 02 = —A — 81//. Substituting these values of 0^ and 0^ in the expression for the ordi-nates of the two projections, and setting them equal for each case,we have as the second condition: Source on temporal sideSource on nasal side x}/ — ^ij/ = {(/ + 1-356 81// = o. A zero value of S-v/r will not satisfy these equations, hence a perfectlysymmetrical eye would have presented to Helmholtz just the phe-nomenon which he observed and any definite conclusion as toeccentricity is excluded. io8 Charles S. Hastings ^ The numerical coefficients of the above equations are, obviously,only correct for the schematic eye and are certainly different for allof the eyes observed. Mo
Size: 2426px × 1030px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookautho, bookcentury1800, bookdecade1890, booksubjectphysiology
