Obituary Notices. ' iii 
Adams’s decisive communications to Challis and Airy), in which the 
outstanding perturbations of Uranus were explained by the action of 
a planet whose position agreed very closely with that indicated by 
Adams. This close agreement by two investigators, each working 
in ignorance of what was being done by the other, at once set 
Professor Challis to work on a search for the planet, but the want of 
a proper star-map necessitated the survey of a relatively considerable 
area of the heavens. In the course of this survey the planet was 
actually seen on August 4th and 12th, 1846, but failing a comparison 
of the observations, it was not then recognised as the object so eagerl}^ 
sought for. That no search was made at Greenwich is explained by 
the simple fact that they had no telescope at all suited to the 
work. 
On the last day of this month of August 1846, Le Verrier sub- 
mitted to the Academy in Paris a third memoir, in which the mass 
of the unknown planet was worked out, together with new elements 
and limiting values for its heliocentric place. Eighteen days after- 
wards, Le Yerrier wrote to Dr Galle, then Encke’s assistant at Berlin, 
asking him to look for the planet in the assigned place, and holding 
out a hope that it might even be recognised by its disc. The planet 
was found the very day, September 23rd, on which Le Verrier’s 
letter reached Berlin. Everything favoured the search — Galle was 
an accomplished observer, the instrument was one of Fraunhofer’s 
masterpieces, and Galle cordially accepted the aid of the young 
astronomer D’Arrest, then a student at the Berlin Observatory. 
D’Arrest contributed notably to the immediate finding of the planet, 
by suggesting the use of Bremiker’s section (Hora xxi.) of the 
Equatorial Star-maps, then in course of publication by the Berlin 
Academy. This very sheet had just been struck off, but had not yet 
been distributed, although a copy was lying at the Berlin Observa- 
tory. Galle estimated the planet’s diameter at about 3", but in his 
letter to Le Yerrier says it was not much to trust to, except under 
very favourable atmospheric conditions, and adds, ‘‘c’est principale- 
ment la carte qui a facility la recherche.” The place of the stranger 
was accurately determined by midnight, and again on the following 
evening, when it was found to have moved about 64 seconds of arc 
in the interim. From Dr Galle’s letter it is also interesting to find 
that Bremiker’s map was not the only new publication pressed into 
