OF SOME OE THE STARS AND NEBITLiE. 
581 
a velocity sufficient to alter its colour sensibly to the eye, still no change of colour would 
be perceived, for the reason that beyond the visible spectrum, at both extremities, there 
exists a store of invisible waves which would be at the same time exalted or degraded 
into visibility, to take the place of the waves which had been raised or lowered in refran- 
gibility by the star’s motion. No change of colour, therefore, could take place until 
the whole of those invisible waves of force had been expended, which would only be the 
case when the relative motion of the source of light and the observer was several times 
greater than that of light. 
In 1845, Ballot published a series of acoustic experiments which support Doppler’s 
theory in the case of sound. In the same paper Ballot advances several objections to 
Doppler’s application of his theory to the colours of the stars*. 
This paper was followed by several papers by Doppler in reply to the objections which 
were brought against his conclusions f. 
In 1847 two memoirs were published by Sestini on the colours of the stars in con- 
nexion with Doppler’s theory J. 
More recently, in 1866, Klinkerfues § published a memoir on the influence of the 
motion of a source of light upon the refrangibility of its rays, and described therein a 
series of observations from which he deduces certain amounts of motion, in the case of 
some of the objects observed by him. 
The method employed by Klinkerfues has been critically discussed by Dr. Sohncke ||. 
It may be sufficient to state that as Klinkerfues employs an achromatic prism, it does 
not seem possible, by his method of observing, to obtain any information of the motion 
of the stars ; for in such a prism the difference of period of the luminous waves would be 
as far as possible, annulled. It is, however, conceivable that his observations of the 
light when travelling from E. to W., and from W. to E., might show a difference in the 
two cases, arising from the earth’s motion through the ether. 
Father Secchi has quite recently called attention to this subject^]". In his paper he 
states that he has not been able to detect any change of refrangibility in the case of 
certain stars, of an amount equal to the difference between the components of the double 
line D. These results are in accordance with those obtained by myself and Dr. Miller 
in 1863, so far as they refer to the stars which had been examined by us. 
Father Secchi’s method of using an unrefracted image as a fiducial mark with di- 
verging rays passing through the prisms might, it is conceivable, be open to objection. 
* “ Akustische Yersuche auf der Niederlandischen Eisenbahn nebst gelegentlichen Bemerkungen zur Theorie 
des Urn. Prof. Doppler,” Pogg. Ann. B. lxvi, s. 321. 
f See Pogg. Ann. B. lxxxi. s. 270, and Pogg. Ann. B. lxxxvi. s. 371. 
X Memoria sopra i colori delle stelle del catalogo de Baily osservati dal P. Bane Sestini. Roma, 1847. 
§ “ Eernere Mittheilnngen iiber den Einflnss der Bewegung der Licbtqnelle anf die Brechbarkeit eines Strahls, 
von W. Rlinkereues,” Nachr. K. G. der ~W. zu Gottingen, No. 4, s. 33. 
|| “ Ueber den Einfluss der Bewegung der Lichtquelle anf die Breebung, kritische Bemerkungen zu der Ent- 
deckung des Hrn. Prof. Klinkerfues. Yon Hrn. Dr. Sohncke, Astron.” Nachr. No. 1646. 
If Comptes Rendus, 2 Mars 1868, p. 398. 
