New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1877-04-27
ACADEMY OF SCIENCES.

A NOVELTY IN SPECTRUM ANALYSIS.
TIE suns RoTATION-ATMosPhERrc DISTINGUISHED
PROM SOLAR LINES IN IRE srECTRUM-AN
ESSAY UpoS THE QUESTION or THE EARrHs
INTERIOR FLUIDITY.
IyRoM 4 STAFF CORRESPONDENT OF THE TRIBuSE'i
WASHINGTON, April 20.-The following
papers read before the Academy of Sciences nave deem
nrevousy alluded 10 IN this correspondence. Their I'M
portance makes them worthy Of a separate letter;
Prot s. p Langley of the Allegheny Observatory III
Introducing his essay describing al Proposed Ne"
Method OF solar Spectrum Anayss" explained 'ha' III
so emitting it he believed. and so far RS nc couiu
ascertain was justified in believing that 'he
method In this special application OF was
quite new The process consists not meIeiy
in placing in juxtaposition, simultaneously UNI
speota OF light from two opposite edges OF the suns
disk (which has been done before but in also deterhh
ing that when these images obtained from the east
and west sides of disk respectively the solar lines 90
not quite coincide, while the atmospheric lnes 90 com
eide The small difference in the position OF the SOAR
lines in the two spectra due to the suns rotation on us
axis causing the of Light on the one side TO be re-
treating from and on the other side to be approaching
the spectators whence there is difference IN the lengths
of tine respective sets Of light waves which give the solar
lines and this shown by the difference OF the position
OF those lines in the spectrum Prof Langley docs h"
OF course claim the juxtapOston Of spectra as nov
city: does propose 10 dDlIt ono Jot vi
that due to Prof c. A. Young for cOnclusiye dem
onstratng that tho difference Of lengths referred TO
can be Independently measured ana he suns rotation
be thereby proved.
No discovery OF modern physical astronomy has a
more striking character than the measurement OF the
speed OF motion OF a celestial body by means OF tAe -
ference OF the wave lengths of its light from that oil
fixed standard 1t is popularity understood that the
motion toward or from of certain fixed stars has thus
been completely demonstrated. Those who are engaged
in these studies, however, are well aware now lar
astronomers have been TIL lately from the certainty
which has been popularity conceded Only last Aplh
Father Secci called attention 10 Van der WEen De
niai on theoretical grounds of the praccabity OF such
demonstration. and added thereto his own doubis'
founded chiefly the dangers of instrumental error
Ii may be admitted that in making such OBSERVATIONS
on the stars there formidable difficulties and num'r
Gus obscure oerrOr Some OF these difcui1'S
are obviaed though others encountered, in obseIv-
ing the difference OF lengths III the hSHt r0m Tie
two sides of the The dinereuce OF veoeltes
here to be measured is nearly Dig English miles
per second THIS though great In itself, ~ very sinai
compared with the speed OF light and tbs relative small
ness occasions the chief difficulty in the measurement
Prot Young has illustrated this by stating the WlOe us
placement Of lines equal to one 77h OF The DIS
lance between ID lines between One-seVenu ana
onephth OF one division Of AugstT0ms scale. ZOneT.
Secch and Hastings have nevertheless thought tna' heS
detected change in the rcfranGbity OF TIE Ilsh ana
VOge using XOiucr's TeyelsiOn SpCctrOscOc oDtheu
displacement of from .OS TO OLD of one OF AngStr0mS
units Finally Prof Young, using RutheriuId graf
Ing showed a vclocty of the suns equator Of In AZ
at The same time showing thai independent measure
mens of the solar and atmospheric lines gave different
results for these two classes This last research was so
much more Systematic aud satisfactory than its preAe-
cSsors that II has turned the weight OF scieDtfic 0-
ion in favor of the view that the change OF wave length
caused by the motion Of luminous body IA real ana
may even be used as a measure OF that motion.
The method proposed by Prot. Langley for the meas
urement difference of wave lengtn has the advant-
are OF being largely free from liability instrumental
errors Indeed an essential feature of this method Is
the security against such that is furnished 10 me
contamination Of two classes of lines which under Ike
instrumental conditions, betray their diverse origin III
1873 in the course research upon the seleotNe
ABSORPTION OF solar atmosphere Prof Langley ar
ranged auuaratus tor comparing homogeneous light from
different part, Of the solar disk The result was chiefly
accomplished by the OF two pairs Of rSht-'need
prisps of totaI reflection disposed in connection
with spectroscope that there could be formed
side by side the spectra of light from different
parts OF the sun; AID by a photometrc dppara-
tus the relative ntensitlcS Of t at different parts OF
these spectrS could De compared II was noi lhtehdu H
first COMPARISON of Individual lines Ot the spec
trIni-a purpose which somewhat similar arrange
mems bad boon used by LOckytr Hastings and perhaps
Ohers-bUt the iIy siaiOus ot Prof Young suggested
Prot Langley another and cOSnate method OF testhS
the principle OF Dupllcr t. Winch this apparatus Is
especially sd pted The theory OF tie proposed method
Is very simple.