An introduction to astronomy: designed as a text-book for the use of students in college. By Denison Olmsted ...

2 1215'iTE PLIANETS'.
series, )beilng rlnoved friom tlhe suni to tile immellnse distance of
nearly ot000 millions of miles (2,80B2,40 f,000). Its diameter is a
little less tllan thlat of Uranus, being 31,000 lnilcs.' Its volume
is nearly sixty times tlhat of thle earth. ]Its periodic time is:16- years, whlich is albout twice that of Uraluss. Its orbit is
nlearly circular, and buit little ilclined to the ecliptic (1L 4t').
Tihel discoverl') of the planet iNeptune is the most remiarkable':astroliomict l event of our tinCes, and is generally considered
as thle most extraordinary dliscovery ever malde in phy1sical
sciencce. IThe leading steps of the process were as follow\s.
T'le p)lanet Uralnus had long been known to be subject to ccrtain irregulalities ill its revol ution aroundl the sunl, not accounted
for by' ll tlhe klnown causes of perturbation. In somle cases
the deviation friom thlte ilr place, as given by the tables, dif.
fcrs f'om actual observation twQo mii tes of a cgrc....... a qualltity indecd whichl seemC s small, but wh}ich is still far greater
than occurs in the case of tlhe otlher plancts, and far too great
to satisfy the extreme accultracy required by modern astronomy.
Thills fitct lolg since suggested to astronllomers tlhe possiblility of
one Or ilmore additional planetsi, hitherto uillitiseovered, wh\ich,
by their attractions, exlert oni U'ralls a great disturbing iftluelnce. Ic Vecrrier, a (distinguislhed FIrenchI astronmlncr, assu1-11l
ing the cxistence of suchI a plalet, a)pplied himisellt; by tle:aid
of the calculus, guided by the law of univer sa gravitation, to
tihe inquiry wlhire the hidden l)lattet was situated -— lt what
distance from the sun-........ and at whlat point of the starry lheavens? ]from Bodo's law of the planlctary distalices (Art. 2.99),
according to whichlt Saturn is nearly tice as far fi'ont the sun
as Jupliter, and Uranus t sice as ftr as Saturn, he inferred thlat,
if a pltnct exists beyond Uranus, its dist-ance is priobably about
twice that of'Jranlus or abott 3,600 nmillions of mliles frVom tlhe
sill, whitch is nearly thirty-eight times tlhat of the eartht. Ii'e
assumed it, however, to be thirty-six times the eartl's mean
listanliee. T'l e corresponding' periodic tilte would be 21 6 years.
After reasoning from analogy, and tle tdoctrine of universals
grtavritation, reslpecting tle 1)osition and mass whic}1 a bo(dy
lmust have in orer to accountt for the perturbations of Uranusl
equations were flormled blctween tlhese 1)elrtulrbatiomsl and thll......................................................................................................................................................