Chemistry and Phystes. 151 
the proportions of the a should be varied with the dimen- 
sions = the tube. With a tube 3 cms. in diameter and 20 cms. 
long, containing one ere of hydrogen and one of air, lines 
appear, pire fern-leaves. With tubes of less diameter the 
effects are more regular, especially if a musical sound is produced 
by the explosion. F ine strie are then observe perpendicular to 
¢ 
defined. If the mixture is ignited by the eudiometric method, 
these appearances are no longer produced, If the tubes are open 
at both ends, the effect is the same as if one end is ee With 
a long tube the appearance in the dark is the same as that of a 
Geissler tube illuminated by a single motion of the Seong — 
ana de Physique, iv, 138. its 
Changes in Light due to the motion of the i is pete 
or of the Observer.—M. Mascarr has examined this question both 
experimentally and shaonctiagihs Arago announced that the 
refraction of the light of two stars. toward one of which the 
earth is approaching and from the other receding, was the same, 
and Fresnel showed that this could be accounted for if part of the 
ether was transported with the refracting medium, the change in 
refraction in fact being compensated by the motion of the teles- 
cope. Many efforts have been made to show optically the motion 
of the earth. Babinet thought he found a solution in the diffrac- 
does not take place. This experiment, repeated under the most 
favorable conditions, both with solar and with artificial light, yields 
from a mirror acts peat as if it came from a source on the pro- 
longation of the ra But this is not correct if the mirror moves, 
as is the case on she: earth, but the conditions are the same as if 
the mirror was itself Juminous, or as if a terrestrial source of light 
was employed. Accordingly, as experiment shows, negative 
results only are obtained. 
Suppose that we have two sources of light, one the soda flame, 
0 
time of vibration of the two sources are identical, but the wave- 
lengths of the light emitted are different, owing to the motion of 
the first. The —— of the two rays oug t, therefore, to be 
different. To t 
ee one fixed with the collimator turned to the west, and 
Obs 
that the desuains was who rolly Paracinhie although a displace- 
ment of a twentieth of that given by Fresnel’s formula would have 
