232 D. P. Todd—wsearch for a Trans-neptunian Planet. 
Superintendent of the Naval Observatory, and Professor Hall, 
in charge of the great refractor. It was with this instruament— 
the 26-inch equatorial—that the search was conducted, begin- 
ning on the night of the 8d of November, 1877. It seemed to 
me that I should begin the search at a point about 20° preced- 
ing that indicated as the most probable position of the planet, 
and continue it to a point following by the same distance. 
But a careful search extending over a zone of this length, and 
of sufficient width to be certain to contain the supposable 
arrive at no successful result from the search of this limited 
zone. 
I may remark that the detailed plan of the instrumental 
light with the appearance of an 
average star of about the thirteenth magnitude. I considered 
tection of a disk of this diameter: in the actual search, a 
power of 600 was often employed, but most of the search was 
conducted with a power of 400 diameters. 
On thirty clear, moonless nights, between the 8d of Novem- 
ber, 1877, and the 5th of March, 1878, this search was carried 
on after the manner I have indicated. 
