824 C. A. Young—Displacement of lines in the 
vision ; after this no adjustment of either telescope or spectro- 
scope was touched in the slightest until the observation was 
limb was brought to the slit, and the micrometer readings were 
repeated, running down and back twice, so as to give four read- 
ing possible constant errors) was found to be about ;%, of one 
nated by inverting the spectroscope, i. e., rotating the 
spectroscope 180°, around the line of collimation; this, how 
ever, in one of the series of readings always brings the ey 
piece into an inconvenient position. One set of observations 
: : ‘ ions are as 
e formule employed in reducing the observations * 
