664 C . G . ABBOT. [J.F.I.

interior are pouring out toward the exterior in forms similar to a water-spout. They are cooled by expansion as they reach the surface, and the partial vacuum formed in the centre of the whirl sucks in the superincumbent and very light gases, hydrogen and calcium, above the sun's surface. The magnetic field found by Hale in sun-spots is due , no doubt, to the rotation of the elec- trically-charged material in the spots. The solar spectrum, with its numerous dark lines, is due to the presence of the gases of the chemical elements which are found upon the earth, rfhese gases are cooler at the boundary of the sun than they are within, where the principal part of the light comes from, hence, as noted above, the effect will be to produce dark lines on a bright background. The irregular mottled appearance of the sun's surface is probably due to differences of temperature which exist in so great a body, and thereby produce variations in brightness of different parts.

It is impossible to go further and touch upon the very inter- esting questions connected with the sun's place among the stars, the dependence of plant growth upon solar radiation, and the relations between the temperature of the earth and the radiation of the sun. These matters, and many details, which it has been impossible to mention in this short account, are discussed by the writer in a book entitled " T h e Sun," to which and to the original sources of information and to longer treatises the interested reader is invited to turn.

Crazing of Lead Glazes o.n Earthenware Bodies. J .A . CALL- COTT. (Trans. Eng. Ceram. Soc., xiii, 49.)--Crazing may be caused by excess of some constituent in the glaze or body, by application of the glaze to too porous a body, or by incorrect firing. ]t is generally due to excess of soda in the glaze or of china clay in the body. Lime may be substituted for soda if.opacity and dullness do not follow, a consequence which is avoided by rapid cooling from tooo ° to 500 ° C., during which crystallization is most .likely to take place. Cornish stone is a useful substitute for soda. China clay in the body may be replaced by Cornish stone or flint, or, if color be no object, by ball clay. Substitution of buff for purple Cornish stone in the body may be a cause of crazing. The function of flint is to alter the coemcient of expansion and to promote chemical combination between clay and fluxes. Vitreous bodies, usually deficient in flint, are especially liable to exhibit crazing. If the mixings are unaltered, a higher tempera- ture or more prolonged firing is required.