PREFACE . 



points on which he was either doubtful or ignorant, and to 

 Sir Charles Bright for the valuable curve of the resistance of 

 gutta-percha at different temperatures. At the same time 

 he has much pleasure in acknowledging the aid he has 

 gleaned from the excellent works of Wiedemann, Dub, 

 Schellen, Moigno, Blavier, De Castro, and others. 



