IN THE SOLAR SYSTEM. 



79 



of a flat plate, whose plane coincides with the sun's equator. But inasmuch as the 

 maximum heat upon the sun's surface was found a little north of the equator, the form of 

 the ascending current of ether should be rather that of a hollow, frustated cone, whose 

 sides, if produced, would form an exceedingly obtuse angle at the sun's centre. 



If we suppose that the functions of receiving cold ether from the regions of space, and 

 of forcing it again from the sun, divide the surface of that orb into equal parts, the zone 

 from which the current ascends must have a breadth of 30° on each side of the sun's 

 equator. Such a division of the solar surface is, however, inadmissible, for the ether de- 

 scending upon the poles should have its volume so enormously increased by the sun's heat, 

 that the area from which it escaped into space, must have a great preponderance over the 

 regions where the fluid arrives in its condensed state. We may, therefore, conclude that 

 the regions upon which the ether descends are comparatively small. 



The ether which ascends from the regions remote from the equator, must have initial 

 directions deviating much from the plane of that circle ; this should make the thickness of 

 the ascending current, near its origin, as great, or greater than the diameter of the sun. 



But this thickness we cannot suppose could continue; for, as the ether advances into 

 the region of the planets, its expansion should be counterbalanced by a loss of thickness. 

 The immediate cause of the flattening being the pressure of the cold ether on the two 

 sides of the plate. 



With the flattening of the ascending current, we may look for the effect of the position 

 of the line of maximum heat upon the sun's surface. 



An analysis of Secchi's observations leads to the conclusion that the line of greatest 

 heat is at the distance of 1° 29' 06" north of the sun's equator* 



* The purpose of the following demonstrations is threefold. Firstly, to show the relations which the axis and 

 equator of the sun bear to the ecliptic. Secondly, to picture the appearance which the sun presented to Secchi at 

 the time of his observations. Lastly, by trigonometrical measurement to determine, with Secchi's observations as 

 data, the position of the line of maximum heat upon the sun's surface, with reference to the solar equator. 



Fig. 1 is designed to show the positions of the equator and axis of the sun in relation to the ecliptic. A B 

 represents the plane of the ecliptic, V P' its polos. The circle is the sun's disc, 

 F 11 its equator, and N S its axis. 



The time of the year when the parts appear in these relations, is about the 6th 

 of June. N C P is the angle by which the sun's axis is inclined to the poles of 

 the ecliptic, about 7°. 



As the earth revolves in its orbit, the sun's axis apparently describes a circle 

 about the poles of the ecliptic. 



All this will appear more clear by viewing the solar system from a point in 

 space opposite its northern face. 



In Fig. 2, the smaller circle represents the sun ; the larger one the earth's orbit. E is the earth, on the 21st 

 March. P is the pole of the ecliptic, N the north pole of the sun, inclining towards longitude 345°. If the 



