THEOPENSPACEINORION 251thanthesupernalvisionoftheinteriorofthecavern—
theabyss,thechasmininfinity.
"ThenebulaofOrioniswiderinangulardiameter
thanthemoon, whosediameteristhirty-twominutes
ofarc. Cutoffalloutlyingstreamers,andtreatmathe-
matically a diameter ofthirty-two minutes,and the
distance and dimensions of thenebula at once sub-
merge humanthought asbyaflood frominfinitude.
'Theopeningofthisrecessisatleastfifteenminutes
ofanarcindiameter;andwiththisvalueletthemathe-
maticalresultsobtain.
"Ifwelookatanyshiningpointinthisnebulaina
powerfultelescope,andmeasureits positionwithex-
ceedingaccuracyby means of a micrometer,to-day,
and repeatthe process six monthslater, amost as-
tonishing discovery will be made; namely, the two
positionsareexactlythesame. Buttheearth,during
thesixmonths, hasmovedtoa distancefromwhere
it wasat first of 186,000,000 miles. See whatthis
means. Takethe sametelescopetothenebula,turn
andlook this way;then the diameterof theearth's
mightyorbit,aline186,000,000mileslong,wouldap-
peartobesoshortthatitcouldnotbemeasuredwith
the micrometer, an instrument able to measure the
diameterofafinehair.
"Buttheopeningofthecaveisatleastfifteenmin-
uteswide. Howfinditswidthinmiles? Thisisim-
possible by measuring any shining portion of the
nebula;sowemustmeasurenear-by stars, andthen
assume that theadjacent nebulais attheir distance
fromtheearth. Someoftheseneighboringstarsare