viii PREFACE 



Bunsen's burner (1866) has been removed, it is hoped finally, 

 from Dumas's apparatus for the composition of water (1841), 

 and the big spirit-lamp has been restored to its place ; and 

 Lavoisier's red-hot gun-barrel is again sealed with clay joints 

 instead of with rubber. The temptation to reconstruct early 

 apparatus (which has led to the association of the Bunsen 

 burner with Lavoisier's work) has been resisted even in the 

 pressing case of Cavendish's experiments on the composition 

 of water, where the gap has been filled by reproducing the 

 contemporary apparatus of Monge ; only when the text and 

 illustrations were complete was the discovery made that two 

 of the globes used in these experiments are still preserved in 

 the library of the Royal Institution. The single case in 

 which a figure has been consciously modified is a small 

 alteration in Priestley's blackboard and table (Fig. 19 b} 

 with the view of making the most of the limited space avail- 

 able for reproduction. 



An exact historical narrative, such as is here presented, 

 could not have been written without free access to books and 

 journals, many of which are rare and some almost inacces- 

 sible. I wish to express my indebtedness to Mr. A. H. White, 

 of the Royal Society's Library, and to Mr. F. W. Clifford, 

 the Librarian of the Chemical Society, for their invariable 

 courtesy and helpfulness over a period of several years, as 

 well as to the Institution of Electrical Engineers for access to 

 their important collection of Volta's papers. I am indebted 

 to the late Miss Freund for a quotation from a copy of 

 Wenzel's Theory of Affinity in the library of the University 

 of Bonn, to Prof. Victor Henri of Paris for some information 

 in reference to early French publications, and to Prof. Ernst 

 Cohen of Utrecht for a number of historical details. The 

 early chapters of the book were written in collaboration 

 with the late Mr. G. C. Donington, whose double qualifica- 

 tion in History and Natural Science gave special value to 

 his opinions and criticisms. I have also derived great 

 benefit from the expert advice which Prof. R. A. Gregory 



