different occasions on which I have observed Jupiter closely 

 when this spot should have been seen. In several of them it 

 should have been near the middle of the disc. Even considering 

 its longitude 240 deg. (as Mr. Dennett has done), it could not 

 possibly have passed out o£ sight by axial rotation. I cannot 

 think it could be present and escape my attention, unless its 

 character had wholly changed; for anyone who sees it now 

 and as it teas on July 9, 1878, a year ago, will at once detect it 

 on any part of the disc. For instance, on the morning of July 

 2, 1879, as soon as my eye glanced on the disc I recognised it, 

 though seen very obliquely to the line of sight and seen unex- 

 pectedly after the lapse of a year. Now, whether this spot has 

 periods of 'recurrence,' as Mr. Trouvelot suggests, or whether 

 at certain times it has a very rapid proper motion on the sur- 

 face of the planet I cannot pretend to determine. On July 9 

 of last year I saw it extend beyond a white spot north of it, 

 but which was in motion is unknown. . . . It is important, 

 I think, to remember that both preceding and following the 

 observation of July 9 the belt region was in a state of unusual 

 agitation." I think that, taking into consideration Mr. Den- 

 nett's observation of July 27 and our own on August 4, 9, and 

 13, we may safely assert that the red spot was visible from July 

 9 (the first record we have of its appearance), until August 13. 

 Then the question naturally arises, " Did this spot suddenly dis- 

 appear between August 13 and 15, on which latter date Pro- 

 fessor Pritchett failed to see it, although it should have been 

 plainly visible ?" If so, it is a most extraordinary occurrence, 

 especially considering its enormous size. Then, as to the other 

 hypothesis, " Could it have had an enormous proper motion at 

 that time ?" Of course it must be borne in mind that at pre- 

 sent it is impossible to ascribe a proper motion to auy spot on 

 Jupiter, for astronomers have not yet satisfactorily settled 

 which particular spots belong to the planet itself, and which 

 are moving on its surface, and hence are unable to fix a period 

 of revolution. But still it may be interesting here just to 

 compare two notes, one by Professor Pritchett, already quoted, 

 where he remarks on the motion of the red spot past two white 

 spots in its vicinity, and the other made by Mr. Todd on the 

 night of August 13, lOh. : — " The oval red space on the southern 

 bright belt, noted on the 4th, still visible, but not the bright 

 spot on the equatorial cloud belt, but a bright spot very like 

 it precedes it several Jovian hours — being near the western 

 edge of the planet, when the red space was rather more than 

 half visible on the opposite or eastern side of the planet." 



At present the red spot looks very similar to what it did in 

 1878 and 1879, although not quite so dark. Its immediate 

 surroundings, however, have altered to a certain extent. If 



