Chase.] 4()g IJuly. 



to Fresnel's theory,* is subject to the laws of inertia and attraction, as 

 well as to those of elasticity. If his theory is correct, the terrestrial 

 ifether (or the portion which partakes of the earth's rotation), maybe 

 so modified by the planetary a3ther (or the portion which revolves 

 about the sun), as to produce a resistance varying at different hours, 

 and a consequently varying atmospheric compression, which may 

 some time enable us to measure its own density. The solar attraction 

 may be constantly tending to accumulate the terrestrial sether, as 

 well as the atmosphere, in a spheroid with a major axis in the line of 

 the radius vector, and the position of the axes, as in the case of the 

 ocean and aerial spheroids, may be modified by rotation. It appears 

 to me that one of the most probable results of the rotation of the 

 earth with its atmosphere, in an aethereal medium, would be the pro- 

 •duction of two systems of oscillations, moving with the rapidity of 

 light, one in tbe'line of the earth's orbit, and the other in the line 

 of its radius vector, and that those systems would be constantly so 

 related that while one tended to retard, the other would tend to 

 accelerate the earth's motion. 



The influences of rotation and attraction can be calculated, and 

 .after deducting their amount, the problem of accounting for the re- 

 sidual disturbance will be simplified. Or, by taking the average of 

 •a long series of observations made at each hour of the solar day, the 

 effects of lunar attraction may be so far eliminated, that they can be 

 eafely disregarded in attempting to fix the approximate value of the 

 other principal disturbances. f The formula for the rotation tide has 

 tilready been given, and observation appears to indicate that it is re- 

 tarded about an hour by inertia ; next in order of importance are the 

 temperature and vapor tide, and the solar tide. It would be pre- 

 sumptuous in the present stage of our investigations, to attempt to 

 fix the precise amount of disturbance which is attributable to each of 

 these two tides, but from the following considerations we may derive 



* It i.s perhaps, hardly proper to call this " Fresners theory," since it follows 

 necessarily from the conception of an extremely tenuous and elastic material 

 fluid, such as the asther is generally supposed to be. But I believe M. Fresnel 

 has done more than any one else to show the agreement of the hypothesis with 

 observed phenomena, and his labors deserve to be kept in honorable remem- 

 brance. 



t The absence of any long series of observations at each hour of the lunar day, 

 prevents our eliminating the effects of solar attraction in a similar way. Never- 

 theless, I propose at some future time to attempt the elimination, so far as prac- 

 ticable with the tables at my command, in the hope of thereby effecting a more 

 accurate determination of the temperature and vapor tide. 



