

PREFACE 



THE Theory presented in the following pages was 

 first sketched by the author in a Paper* communi- 

 cated to the Royal Irish Academy on the i3th of 

 November, 1871. This Paper was followed by 

 others, f in which the subject was more fully 'de- 

 veloped. The entire Theory has been re-written, 

 and systematically arranged, in the present volume. 



We owe to the geometrical ability of Poinsot 

 and Chasles the two fundamental theorems from 

 which this subject takes its rise. To the labours 

 of Pliicker, and his school, we are indebted for the 

 theory of linear geometry, which receives a physical 

 interpretation by the Theory of Screws. 



References are made in the foot notes, and more 

 fully in the Appendix, to various authors whose 

 writings are connected with the subject discussed in 



* Transactions of the Royal Irish Academy, Vol. xxv., pp. 

 157-217. 



f Philosophical Transactions of the Royal Society of Lon- 

 don, Vol. clxiv., pp. 15-40. Transactions of the Royal Irish Aca- 

 demy, Vol. xxv., pp. 295-327. 



