
Occurrence of Cavitation in Lubrication. 329 
| Wote.—These experiments were repeated during the early 
part of February, 1904, when the earth’s orbital velocity 
conspires approximately with that of the solar system in 
space. The conditions for observation were quite as favourable 
as before: but no effect could be detected. With glass, the 
optical system was rotated through several quadrants con- 
secutively so as to observe any possible trace of an effect. 
Observations were made at noon and at 6 P.M, 
Hicks *, in a more rigorous discussion than that of Lorentz, 
of the effect to be expected in the Michelson-Morley expe- 
ee 
Zye m a 
direction of drift, there should be an elongation of 7V2 
to account for the negative results of the observations. The 
experiment itself should thus disprove the FitzGerald- Lorentz 
hypothesis. Hither, on any of the suppositions possible from 
Lorentz’s point of view, viz. contraction along the drift and 
zero change at right angles, no contraction but extension at 
right angles to the drift or elongation along and at right 
riment, shows that instead of a contraction of 
angles to the drift, such that the difference is — r, on the 
v 
aye ° 
conclusion of Hicks, the effect to be observed by means of 
double refraction in the preceding experiments would be the 
same.—D. B. B.] 
XXXVIII. On the Occurrence of Cavitation in Lubrication: 
By 8. Sxiyner, VM_A., University Demonstrator of Experi- 


mental Physics, Cambridge fT. V 
_Plates X VII.—XIX. | 
§ 1. HE following experiments } arose from an obser- 
vation made when determining the refractive 
index of a liquid by means of Newton’s rings. As Newton 
showed, the rings can be obtained when a liquid is run into 
the space between the lenses (Opticks, Obs. 10); and by 
comparing the radii of the rings with those obtained with 
the same lenses and air we have a means of measuring the 
refractive index between air and the liquid. The only 
difficulty is to arrange the illumination suitably as the rings 
are far fainter with the liquid than with air. 
* Phil. Mag. Jan. 1902. 
f Communicated by the Physical Society ; read November 27, 1903. 
¢ These experiments formed the subject of a Demonstration before 
the Cambridge Philosophical Society, November 10, 1902. 
