DIFFERENCEINGLORY 197
sunmanysubstancesknowntoexistintheearth,and
somethatwehadnot discoveredwhenthesunwrote
theirname, orrathermade their mark, in thespec-
trum."—H.W.Warren.
"The readernowunderstandsthatwhenthe Hght
froma celestialobject isanalyzedbytheprism,and
thecomponentcolors are spread outsingly as on a
sheet,thedarkandbrightlineswhichweseearethe
lettersoftheopenbook whichwearetoread soas
tolearnwhattheytellusofthebodyfromwhichthe
lightcame, or the vapors through which it passed.
WhenweseealineorasetofHueswhichwerecog-
nizeasproducedbya knownsubstance, weinferthe
presenceofthatsubstance. Thequestionmaynowbe
asked,Howdoweknowbutthatthelinesweobserve
maybe produced by other substances besides those
whichwefind toproduce themin our laboratories?
Maynotthesamelinesbeproducedbydifferentsub-
stances?
"Thisquestioncanbeansweredonlybyan appeal
toprobabilities. Theevidenceinthecaseismuchthe
sameas thatby which, recognizingthe picture ofa
friend,we concludethatitis notthepictureof any
oneelse. Foranythingwecanprovetothecontrary,
anotherpersonmighthaveexactlythesame features,
and might, therefore, make the very same picture;
but, as a matter of fact, we know that practically
no two men whom we have seen do look exactly
alike,anditisextremelyimprobablethattheywould
everlookso. Thecaseisthesameinspectrumanaly-
sis. Among the great number of substances which