ROLLEDTOGETHERASASCROLL 259Whenwecometoconsidertheeffectoftheatmos-
phereinourviewofthestarryheavens,welearnthat
itisa mattertheastronomersmust takecarefulac-
countof. Thereismoreorlesssmokeintheatmos-
phere, or at least floating particles of dust, which
obscure the sight to some degree. There are also
strataofatmosphereofvaryingdensity. Andallthese
thingshavetheirpartinpreventingsuchaviewofthe
starsaswouldotherwisebepossible.
Onewhohaseverattemptedtostudythestarswith
atelescopeoflargermagnitude, knowssomethingof
thedifficultyencounteredingettingaproperviewof
theheavens. Onemayhavetowaitnightafternight
fora suitabletime,onlytobedisappointed. Tothe
ordinaryobservatory,thereare comparativelyonlya
fewnights in theyearsuitable forthestudy ofas-
tronomy. Oftentimes as onelooksthrough theeye-
pieceofthetelescope,waves oflightaffectedbythe
currentsofairarepassingacrosstheobjectpieceof
thetelescope,causingthestarstodanceinamanner
that is disconcerting and unsatisfactory. All these
thingsgo to show thattheatmosphere toagreater
orlessextentobscuresthevisionoftheheavenswhich
otherwisewe mightobtain. Itis on account ofthe
difficultiesoftheatmospherethatsomanyastronomi-
cal observatories are located upon high mountains,
wheretheatmosphereislessdense, where itis more
uniform,whereitislessaffectedbyheatcurrentsand
lessobscuredbythedustandsmokeofthecities. In
the dry, high air of the mountains, the astronomer
carriesonhisstudieswithmuchlesstocontendwith.