1885.1 
3 
Two Planets beyond Neptune. 
not know that every law has its opposite and unknown ? may 
be therefore deduced from its apparent exceptions ? But 
perhaps he has changed his mind. Besides, his remark 
does not reach my theory, which gives reasons, and em- 
braces the unknown within the origin and history of the 
known. 
When Prof. Pierce taunted Le Verrier that the planet 
lound by Galle was not the predicted, because all elements, 
longitude excepted, were wrong, Le Verrier is said to have 
pleaded that a more distant planet having produced errors 
from 5" to 6" might have led to these mistakes. If this 
reply should have been made, and is not a wrong version of 
a passage from Le Vender's memoirs, we may ask why then 
he did not enquire more closely into the cause of the mis- 
takes ? I shall give quotations from Le Vender's four 
memoirs, read before the Paris Academy of Sciences, and 
published in the “ Connaissance des Temps ” for 1849, and 
shall number them for reference. 
“ On the Existence of a Trans-Uranian Planet.'' 1 
1. “ In the course of the year 1845 Arago represented to 
me that the importance of this question imposed on every 
astronomer the duty to concur in clearing it up to the best 
of his ability.” 
2. “ The theory of Uranus has already given occasion for 
many hypotheses, but without scientific value, because not 
founded on rigorous calculations.” “ Everyone followed the 
leaning of his imagination, without furnishing reasons for 
his assertions.” 
3. Proud of his achievement Le Verrier exclaims on 
October 5th, 1846 : — “ So the position had [been foreseen to 
less than a degree.” “ Thinking of the smallness of the 
disturbances from which the position of the star has been 
inferred, this success lets us hope that after thirty or forty 
years of observation of the new planet it may lead, on its 
part, to the discovery of the next in distance from the Sun, 
and so on.” 
When concurrent signs make it probable that not alone 
Trans-Neptunian planets, but also a lawful organisation and 
a limit of our planetary system exist, should an Arago not 
consider it “ the duty of every astronomer to contribute to 
the utmost of his ability ” towards their discovery ? Be- 
cause the errors of Le Verrier are best evidence for the 
existence and elements of these unknown, I shall point out 
their extent and bearing. 
