40 Prof. Challis's Observations relative to the New Planet. 



cussion of the observations, being much occupied with reduc- 

 tions of comet observations, and little suspecting that the in- 

 dications of theory were accurate enough to give a chance of 

 discovery in so short a time. On Sept. 29, I saw for the first 

 time the communication presented by M. Le Verrier to the 

 Paris Academy on Aug. 31. I Avas much struck with the 

 manner in which the author limits the field of observation, 

 and with his recommending the endeavour to detect the planet 

 by its disc. Mr. Adams had already told me, that, according 

 to his estimation, the planet would not be less bright than a 

 star of the ninth magnitude. On the same evening I swept a 

 considerable breadth in declination, between the limits of 

 right ascension marked out by M. Le Verrier, and I paid par- 

 ticular attention to the physical appearance of the brighter 

 stars. Out of 300 stars, whose positions I recorded that 

 night, I fixed on one which appeared to have a disc, and which 

 proved to be the planet. This was the third time it was ob- 

 served before the announcement of the discovery reached me. 

 This last observation may be regarded as a discovery of the 

 planet, due to the good definition of the noble instrument 

 which we owe to the munificence of our Chancellor. 



From the reduced places of the planet on Aug. 4 and Aug. 

 12, and from observations since its discovery extending to 

 Oct. 13, Mr. Adams calculated, at my request, values of its 

 heliocentric longitude at a given epoch, its actual distance 

 from the sun, longitude of the node, and inclination of the 

 orbit, which were published as early as Oct. 17. I am now 

 diligently observing the planet with the meridian instruments; 

 and when daylight prevents its being seen on the meridian, I 

 propose carrying on the observations as long as possible with 

 the Northumberland equatoreal, for the purpose of obtaining 

 data for a further approximation to the elements of the orbit. 



My report of proceedings relating to the planet here termi- 

 nates. I beg permission to add a few remarks, which the 

 facts I have stated seem to call for. It will appear by the 

 above account that my success might have been complete if I 

 had trusted more implicitly to the indications of the theory. 

 It must however be remembered that I was in quite a novel 

 position : the history of astronomy does not afford a parallel 

 instance of observations undertaken entirely in reliance upon 

 deductions from theoretical calculations, and those too of a 

 kind before untried. As the case stands, a very prominent 

 part has been taken in the University of Cambridge, with re- 

 ference to this extension of the boundaries of astronomical 

 science. We may certainly assert to be facts, for which there 

 is documentary evidence, that the problem of determining 



