"There is every reason for believing that the radiations which constitute heat and light are essentially the same." "Gravity acts instantaneously." _Static Electricity._ 12. (Page 52.) Speaking of static electricity, FARADAY remarks: "What an idea of the ever-present and ever-ready state of this power is given to us, when we consider that not only every substance, but almost every mode of dealing with substance manifests its presence. It is not accidental at these times, but active and essentially so, and we may, in our endeavors to comprehend it, usefully compare and contrast it with gravity which never changes. There we see that power which in undisturbed and solemn grandeur holds equally the world and the dust of which worlds are formed together, and carries them on in their course through illimitable space through illimitable ages; and in this other power, even in this our first glimpse we see probably the contrasted force which is destined to give all that vivacity and mutual activity to particles that shall fit them as far as matter alone is concerned, for their wonderful office in the phenomena of nature, and enable them to bring forth the ever varying and astonishing changes which earth, air, fire and water present to us; from the motion of the dust in the whirlwind up to the highest conditions of life." 13. (Page 61.) An illustration of this form of wind-production may be found in the following facts related by DR. GISLER, who for a long time dwelt in the north of Sweden: "The matter of the aurora borealis sometimes descends so low that it touches the ground. At the summit of high mountains it produces upon the face of the traveller an effect analogous to that of wind." We should pronounce this effect to be the production of a true wind of a circumscribed or local character. _Solar Spectrum, its origin._ 14. (Page 80.) PROF. KIRCHHOFF was led to the study of a coincidence between the bright yellow line given in an incandescent sodium vapor, and the solar line "D," which coincidence had already been noticed by FRAUENHOFER. Upon applying a greater dispersive power he noticed that the line "D" was a double one; but so also was the sodium line under these conditions. Moreover, each line of the one coincided with each line of the other. The _suspicion_ became strong that it was the sodium in the _sun_ which caused the "D" line. He then extended the comparisons to other elements. He carefully measured sixty bright lines in the spectrum of iron; and found every one of these sixty lines to correspond with a dark in the solar spectrum. "The overwhelming _probability_ of a common cause for both was forced upon him, and _by calculation_ he ascertained that this probability was as one million million million to one, in its favor."--LOCKYER. ADDENDUM.