204 PETER GUTHRIE TAIT 



" The credit of breaking up the monopoly of the great masters of the spell, and 

 making all their charms familiar to our ears as household words, belongs in great 

 measure to Thomson and Tait. The two northern wizards were the first who, with- 

 out compunction or dread, uttered in their mother tongue the true and proper 

 names of those dynamical concepts which the magicians of old were wont to invoke 

 only by the aid of muttered symbols and inarticulate equations. And now the 

 feeblest among us can repeat the words of power and take part in dynamical 

 discussions which but a few years ago we should have left for our betters. 



" In the present edition we have for the first time an exposition of the general 

 theory of a very potent form of incantation, called by our authors the Ignoration 

 of Coordinates. We must remember that the coordinates of Thomson and Tait are 

 not the mere scaffolding erected over space by Descartes, but the variables which 

 determine the whole motion...." 



There then followed a remarkably clear statement of the conditions under 

 which certain kinds of coordinates not only may be ignored but ought to be 

 ignored, and the final illustration was in these words : 



"There are other cases, however, in which the conditions for the ignoration of 

 coordinates strictly apply. For instance, if an opaque and apparently rigid body 

 contains in a cavity within it an accurately balanced body, mounted on frictionless 

 pivots, and previously set in rapid rotation, the coordinate which expresses the angular 

 position of this body is one which we are compelled to ignore, because we have 

 no means of ascertaining it. An unscientific person on receiving this body into his 

 hands would immediately conclude that it was bewitched. A disciple of the 

 northern wizards would prefer to say that the body was subject to gyrostatic domi- 

 nation." 



