CONTRIBUTIONS TO SCIENCE. 499 



children in the higher grade schools, so simple that the 

 most casual reader will think that he understands it, while 

 it is the admiration of professed mathematicians, and by no 

 means easy reading for those who expect, or have gained, 

 high places in the mathematical tripos : but as the book is 

 well within the reach of every reader, it is unnecessary here 

 to attempt any detailed account of it. 



But Maxwell's investigations in dynamics were not con- 

 fined to paper. Of the problems suggested to him by the 

 devil on two sticks we have no" account. During his resi- 

 dence in Cambridge he endeavoured to investigate the pro- 

 cess by which a cat is enabled invariably to alight on her 

 feet. The mode of conducting the experiments and the 

 impression they left on the mind of the College will appear 

 from the following extract from a letter written to Mrs. 

 Maxwell, from Trinity, on January 3d, 1870, when Professor 

 Maxwell was examining for the Mathematical Tripos : 



There is a tradition in Trinity that when I was here I dis- 

 covered a method of throwing a cat so as not to light on its 

 feet, and that I used to throw cats out of windows. I had to 

 explain that the proper object of research was to find how quick 

 the cat would turn round, and that the proper method was to let 

 the cat drop on a table or bed from about two inches, and that 

 even then the cat lights on her feet. 



The " Dynamical Top," which was invented by Maxwell 

 to illustrate dynamical propositions, technically so-called, 

 was, in its final form, constructed of brass by Mr. Eamage of 

 Aberdeen. It was this top which Maxwell brought with him 

 to Cambridge when he came up for his M.A. degree in the 

 summer of 1857, and exhibited to a tea-party in his room in 

 the evening. His friends left it spinning, and next morning 

 Maxwell, noticing one of them coming across the court, leapt 

 out of bed, started the top, and retired between the sheets. 

 It is needless to say that the spinning power of the top 

 commanded as great respect as its power of illustrating 

 Poinsot's Theorie Nouvelle de la Rotation des Corps. 



In the work just referred to, Poinsot shows that a body 



