ADDRESS-SECTION A, B.A. 1876. 263 



travelling round of the instantaneous axis rela- 

 tively to the earth in an approximately circular 

 cone whose axis is the principal axis of inertia, 

 and relatively to space in a cone round a fixed 

 axis. In the model the former of these cones, 

 fixed relatively to the earth, rolls internally on the 

 latter, supposed to be fixed in space. Peters gave 

 a minute investigation of observations at Pulkova 

 in the years 1841-42, which seem to indicate at 

 that time a deviation amounting to about {^" of 

 the axis of rotation from the principal axis. Max- 

 well, from Greenwich observations of the years 

 1851-54, found seeming indications of a very slight 

 deviation, something less than half a second, but 

 differing altogether in phase from that which the 

 deviation indicated by Peters, if real and perma- 

 nent, would have produced at Maxwell's later time. 

 On my begging Professor Newcomb to take up the 

 subject, he kindly did so at once, and undertook to 

 analyse a series of observations suitable for the 

 purpose which had been made in the United States 

 Naval Observatory, Washington. A few weeks 

 later I received from him a letter referring me to a 



