12 Mr. WHEWELL on the 
plicated. At any point of time the body may be conceived te 
be moving about some axis or other; but the position of this 
instantaneous axis, as it is called, both in the body and in fixed 
space, may be perpetually varying, as well as the angular velocity 
about it; and the forces exerted by each particle will vary with 
these changes. The first solution of the problem, taken thus 
generally, is due to Dalembert, who published it in 1749 in his 
Researches on Precession and Nutation. Euler, in the Berlin 
Memoirs shortly after, put the solution in a more symmetrical 
and simple form, acknowledging at the same time Dalembert’s 
prior claim to it. The equations however to which the con- 
ditions of rotation are reduced seem to have first appeared in 
the form in which they are now generally presented, in the 
Berlin Memoirs for 1758. The same subject was pursued in 
other Memoirs, and more extensively in Euler's ‘‘ Theorta Motus 
Corporum Solidorum et Rigidorum,” which appeared in 1767. 
Lagrange, in the Memoirs of the Berlin Society for 1773, con- 
sidered the subject on principles more general than his prede- 
cessors. The results, however, of all these different authors, as 
well as of Frisi and others who afterwards treated the question, 
agreed, though obtained by a variety of methods. In the Philo- 
sophical Transactions for 1777, Mr. Landen gave “A new 
Theory of the Rotatory Motion of Bodies, affected by forces 
disturbing such motion.” In this Memoir, he expresses himself 
dissatisfied with the explanations which he had seen on the 
subject; but it does not appear that he was at that time 
acquainted with the researches of Dalembert and Euler, and he 
has not examined particularly the cases in which his conclu- 
sions are at variance with theirs. He afterwards read the 
solutions of his precursors in this path of enquiry, and con- 
vinced himself that they were false; and in the Transactions 
of the Royal Society for 1785 he stated this, and gave his own 
