A Peculiar Clay from near the City of Mexico.

that astronomical observers will probably be able to make a definite decision as to whether or not any of the existing spiral nebulae have developed from bacula or from less regular forms by substantially the same method. Till that is decided further discussion would be superfluous. It is possible that there are well developed spiral nebulae in which mutual interference has done little or nothing to reduce orbits to ellipses of small eccentricity. To such nebulae the analysis here indicated has no application, nor could their motions be formulated in the present state of science.9