NEW PLANETS NEAR THE SUN. 47 



due to a group of planets, ' they are each so small as to be 

 invisible in transits across the sun. They must also,' he 

 proceeds, * be so small as to be invisible during total eclipses 

 of the sun, because they have always failed to show them- 

 selves then.' This remark relates, of course, to naked-eye 

 vision. As no intra- Mercurial planet had ever been searched 

 for systematically with the telescope, before the recent 

 eclipse, there was nothing to prevent astronomers from 

 believing that a group of planets, visible in the telescope 

 during total eclipse, may travel between the sun and the 

 path of Mercury. 



I proceed at once to consider the evidence afforded during 

 the eclipse of July, 1878, not discussing further the question 

 of Lescarbault's Vulcan, because it appears to me so clear 

 that there must have been some mistake, and because later 

 observations seem to throw clearer evidence on the matter 

 than any which had been before obtained. Yet it must be 

 admitted that even now the evidence is not all that could be 

 desired. 



Professor Watson, of Ann Arbor, the discoverer of more 

 than a score of the small planets which travel between the 

 paths of Mars and Jupiter, had been searching for an extra- 

 Neptunian planet, when the approach of the eclipse of July, 

 1878, suggested the idea that he should return for a while from 

 those dismal depths which lie beyond the path of Neptune 

 to seek for a new planet within the glowing region between 

 the sun and the path of Mercury. The occasion was excep- 

 tionally favourable because of the great height above the 

 sea-level from which the eclipse could be observed. Ac- 

 cordingly he betook himself to Rawlins, Wyoming, and pre- 

 pared for the search by providing his telescope with card 

 circles in such sort that the place of any observed star could 

 be recorded by a pencil-mark on these circles, instead of 

 being read off (with the possibility of error) in the usual way. 

 It is unnecessary to explain further, because every one who 

 has ever used an equatorial telescope, or is acquainted with 

 the nature of the instrument, will at once understand Pro- 



