The connection of the physical sciences / by Mrs. Somerville.

  • Mary Somerville
Date:
1834
Catalogue details

Licence: Public Domain Mark

Credit: The connection of the physical sciences / by Mrs. Somerville. Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

    40/364
    ascending node coincides with the equinox of spring, and augments it when that node coincides with the equinox oi autumn. As the. cause must he proportional to the effect, a comparison of these inequalities, computed from theory, with the same given by observation, shows that the com- pression of the terrestrial spheroid, or the ratio of the dif- ference between the polar and equatorial diameters, to the diameter of the equator, is !— It is proved analytically * 305.05. * that, if a fluid mass of homogenous matter, whose parti- cles attract each other inversely as the square of the dis- tance, were to revolve about an axis as the earth does, it would assume the form of a spheroid whose compression is—, whence it appears that the earth is not homogenous, but decreases in density from its centre to its circumfer- ence. Thus the moon's eclipses show the earth to be round, and her inequalities not only determine the form, but the internal structure of our planet; results of analy- sis which could not have been anticipated. Similar ine- qualities in the motions of Jupiter's satellites prove that his mass is not homogeneous, and that his compression is — His equatorial diameter exceeds his polar diameter by about G230 miles. The phases of the moon, which vary from a slender silvery crescent soon after conjunction to a complete circle of light in opposition, decrease by the same degrees till the moon is again enveloped in the morning beams of the sun. These changes regulate the return of the eclipses ; thoseof the sun can only happen in conjunction, when the moon, coming between the earth and the sun, intercepts his light; and those of the moon are occasioned by the earth intervening between the sun and moon when in op- position. As the earth is opaque and nearly spheric;;], it