_Sun-heat._

7. (Page 41.) "The sun, as the main source of heat and light, must be able to call forth and animate magnetic forces on our planet."--HUMBOLDT.

"It is an incontestable fact that the sun exercises an action upon the magnetic phenomena which are manifested upon our globe."--SECCHI.

"What is certain is, that there ought to be, between the sun and planets, a means of communication of force, and the transmission of movement."--_Ibid._

"The central body may, as a powerful source of heat, excite magnetic activity on our planet."--HUMBOLDT.

8. (Page 42.) "It cannot be doubted that electro-magnetic currents exist in the interior of the globe."--AMPeRE.

"The internal heat of our planet is connected with the generation of electro-magnetic currents."--HUMBOLDT.

"A large proportion of winter heat of the poles comes through the equatorial current."--YOUMANS.

_Aurorae._

9. (Page 44.) "HOOD heard a noise as of quickly moved musket-b.a.l.l.s, and a slight crackling sound during an aurora. He also noticed the same noise on the following day."

"FATHER PERRY of the Stonyhurst Observatory remarked that the green spectroscopic line characteristic of the aurora, could be detected even where the una.s.sisted eye failed to notice any trace of light."

"The fleecy clouds seen in Iceland by THIENEMANN, and which he considered to be the northern light, have been seen in recent times by FRANKLIN and RICHARDSON, near the American north pole, and by ADMIRAL WRANGEL on the Siberian coast. All remarked that the aurora flashed forth in the most vivid beams when ma.s.ses of cirrus strata were hovering in the upper regions of the air, and when these were so thin that their presence could only be recognized by the formation of a halo around the moon."

"These clouds sometimes range themselves _even by day_ in a similar manner to the beams of the aurora and then disturb the course of the magnetic needle in the same manner as the latter. On the morning after every distinct nocturnal aurora the same superimposed strata of clouds have still been observed, that had previously been luminous."

PARRY even "saw the great arch of the northern light _continue throughout the day_."

"ARAGO was of the opinion that each observer saw his own aurora somewhat as each observer of a rainbow sees the luminous arc differently placed."

_The Great Sun Battery._

10. (Page 44.) If with a percussion cap and a tear we may develop sufficient power to deflect a magnetic needle 3,000 miles distant, what power may not be expected of the sun, 1,250,000 times larger than the earth; the sun exercising a force of the same character?

_Gravity._

11. (Page 50.) "PROF. MOSSOTTI has recently shown, by a very able a.n.a.lysis, that there are strong grounds for believing that not only the molecular forces which unite the particles of material bodies depend on the electric fluid, but that even gravitation itself, which binds world to world, and sun to sun, can no longer be regarded as an ultimate principle, but the residual portion of a far more powerful force, generated by that energetic agent which pervades creation."--FARADAY.

"If gravitation is made to mean something allied to magnetism, some poorly explained phenomena become easily understood. But what are the circ.u.mstances affording proof of the ident.i.ty of these forces? First, gravitation acts upon all kinds of matter; FARADAY proved the same of magnetism. Second, gravitation is attractive; so is magnetism. Third, gravitation is proportionate to the ma.s.s; the force of magnets also depends upon the ma.s.s. Fourth, gravitation acts in an inverse ratio to the square of the distance; so does magnetism. Fifth, gravitation does not manifest polarity; magnetism is known not to do so. Sixth, gravitation acts independently of bodies affording a resistance to light and heat; so does magnetism."--CARTWELL.

FARADAY'S biographer says:--"He is oppressed with the magnitude and importance of his subject, yet is stimulated by the fact that the discovery which he aims for (the relationship between gravity and electricity) would have a bearing in importance far beyond all conception in elucidating not only the facts connected with these subjects, but also others of a high importance. There being scarcely a limit to the subjects which would be illuminated by it."

"Gravity, surely this force must be capable of an experimental relation to electricity and magnetism and the other forces, so as to bind it up with them in reciprocal action and equivalent effect."--FARADAY.

KEPLER regarded gravity and heat "as being probably derived from one single principle."

"There is every reason for believing that the radiations which const.i.tute 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 s.p.a.ce 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 ill.u.s.tration 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 a.n.a.logous to that of wind."

We should p.r.o.nounce this effect to be the production of a true wind of a circ.u.mscribed 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.

The great Solar Cone-s.p.a.ce, in order to be clearly marked to the eye, was represented in Plate I, page 30, as white. This to some readers may be misleading; as this s.p.a.ce when viewed transversely is not luminous,--it is not even visible. (Pl. V.)

[Ill.u.s.tration: Pl. V. Solar Cone, Or Cone-s.p.a.ce.]

Outside of the atmospheric envelope of all spheres, there is only "_the black of infinite s.p.a.ce_."[E]

Retro-action between the earth and visible and invisible spheres, gives to the earth the light which it possesses during the night-season.

FOOTNOTES:

[E] Flammarian.