1S4 Some Account of the Solar Spots 



each was uniformly surrounded by its umbra. On the 16th, 

 however, an opportunity occurred for examining them when 

 very near the western hmb, and their figure is dehneated in 

 No. 1. Unfortunately, on the I7th the sky was overcast, other- 

 wise the leading spot would have been seen passing the limb, when 

 in all probability an indenture or notch would have been per- 

 ceived. On the same day, too, the obhque position of the spots 

 would have rendered it more easy to discover any alteration in 

 the breadth of the umbra, beyond what the rectilineal view might 

 have occasioned. Previous to the 16th, however, no change 

 was visible, except only that in approaching the limb the spots 

 seemed to become closer together than when near the centre. 

 Further observations, therefore, appear necessary in order to 

 establish Dr. Wilson's theory; which indeed, were the phaeno- 

 mena he describes uniform and constant, would be extremely 

 rational and probable. 



These spots did not reajipear with the next revolution of the 

 sun, as might have been expected, at theend of the month; nor did 

 the disk of the sun present any thing remarkable till the middle 

 of October ; when, on the 16th, two small spots moving in a 

 line were faintly seen near the centre. On the 17th, ISth and 

 20th, they appeared full to view ; and having traversed the disk 

 almost in a line, the foremost passed the western limb on the 

 2l3t, at an angle of about forty-three degrees south of the equa- 

 tor. In general the course of the maculae is, with a little va- 

 riation, parallel to the sun's equator ; but the direction in which 

 these proceeded was very singular and curious. If mechanical 

 causes are sought to account for this peculiar motion, it must 

 be concluded that the spots were impelled Ijy two forces acting 

 at right angles to each other. The revolution of the sun would 

 give line power, in the direction of the equator; but what force 

 could be exerted in a line with the polar axis appears inexplica- 

 ble. See No. 2. 



On November 1st, two spots were seen, the one a little south 

 of the sun's equator, and not far from the line of its axis ; and 

 another somewhat larger in size, north of the equator, and rather 

 nearer to the line of the poles. On the following day (Nov. 2d) 

 the southern spot had advanced, but in an oblique direction; and 

 that to the north had passed over a space more l/ifin equal to 

 one fojtr'h of the diameter of the tiisk,'and was stationed about 

 halfway between the centre and western limb. (See No. 3.) The 

 natine of the sun is so totally unknown, that it is impossible to 

 assign any philosophical reason for this accelerated motion ; but 

 it is obvious from this example, as well as from the circumstances 

 noticed in October (see No. 2), as above related, that the spots 

 are floating substances, not adhering to the surface of the sun ; 



otherwise 



