720 THE POPULAR SCIENCE MONTHLY. 



of Greenwich, and it was easy to prove that it was nothing but a simple 

 sun-spot. 



The fact that the spot was not to be seen the next day seemed to 

 confirm the planetary hypothesis ; but it was not sufficient, since there 

 are ephemeral sun-spots, too. Nor is the roundness of the spot a dis- 

 tinctive character either. The proper movement then remains. Here we 

 must note a circumstance which oftentimes must have caused illusions. 

 When we observe the sun with a telescope not equatorially mounted, 

 and whose support has not the two motions, vertical and azimuthal, 

 as is commonly the case, the position of a sun-spot, by reason of the 

 diurnal motion, is ever changing with relation to the vertical diameter 

 of the disk. Even when an observer has had large experience, it is 

 difficult for him to guard against the belief that the spot has changed 

 its position on the disk. 



This observation, then, had to be disallowed. But there remained 

 others which were not to be discredited on the same grounds, and 

 Leverrier, taking them to be more trustworthy, used them in calculating 

 the orbit of the hypothetical planet. Different interpretations gave him 

 five different orbits, with periods varying between twenty-four and fifty- 

 one days. But he seems to have preferred that which gives a period 

 of thirty-three days, and announced that on March 22, 1877, the planet 

 in question might pass before the sun. Astronomers all over the world, 

 with one accord, observed the sun on that day, to descry the transit, but 

 the result was nil. No black point was to be seen. 



Among the prior observations Leverrier accepts five as certain, 

 viz. : Fritsche's, in 1802 ; Stark's, in 1819 ; Cuppis's, in 1839 ; Side- 

 botham's, in 1849 ; Lescarbault's, in 1859 ; Lumnis's, in 1862. One of 

 the best is no doubt that of Dr. Lescarbault, a country doctor, with a 

 passion for astronomy, and who had vowed to the study of the heavens 

 the time which was not spent in alleviating the wretchedness of earth. 



This amateur astronomer, while observing the sun on March 26, 

 1859, from his humble house at Orgeres, discovered on its radiant disk 

 a round, very black spot, which he was able to study for over an hour, 

 and the proper motion of which he thus determined, no doubt tak- 

 ing account of the causes of error to which we have alluded. It was 

 during this same year that Leverrier perceived the necessity of in- 

 creasing by 38" the secular movement of Mercurj's perihelion, and 

 offered the hypothesis that a planet nearer to the sun than Mercury 

 would account for the difference. Thus the observation made by my 

 old and learned friend came as though on purpose to confirm the 

 theor}', just as earlier the telescopic discovery of Neptune had come to 

 confirm so brilliantly the theoretical discovery of that distant planet. 



"VVellnigh twenty years have passed since 1859, and yet a fact 

 which one might have supposed would be speedily confirmed, owing to 

 the rapidity of the planet's revolution, and its no doubt frequent tran- 

 sits across the sun — this fact has received no confirmation. Yet search 



