HIS INFLUENCE IN NATURAL HISTORY 251 



greatest work in this field being his lectures for the Gilchrist 

 Trustees. He mentions that from 1874 to 1880 he delivered 

 158 of these lectures in 61 towns, and he continued this work 

 with equal activity for another 10 years. He was a vigorous 

 and effective lecturer, who always interested his audience ; he 

 illustrated his lectures by bold diagrams, drawn by his own 

 hand. In order to form any idea of Williamson's many-sided 

 activity it must be remembered that he was all the time engaged 

 in active medical practice, both general and special, for he was 

 well known as an aurist. Yet he always found time for fruitful 

 original research, often of the most laborious character. 



Prof. Judd says, in a letter written to me in February 1911: 



"I have often been struck by the fact that Williamson, 

 appointed to an impossible Professorship of Zoology, Botany 

 and Geology, managed to initiate great movements in connection 

 with each of these sciences. 



" In Geology he was clearly the pioneer in the subdivision 

 of formations into zones each characterised by an assemblage 

 of fossils Ammonites playing the most important part.... But 

 Williamson did another great service to Geology.... Sorby visited 

 Williamson at Manchester and learned the art of making sections 

 which he applied with such success to the study of igneous and 

 other rocks, becoming the 'Father of Micropetrography.' 



"In Zoology, Williamson initiated the work done in the 

 study of deep-sea deposits, by his remarkable memoir on the 

 mud of the Levant, in 1845, when he was 29 years old. This 

 led to his study of the Foraminifera (especially by the aid of 

 thin sections) and to his monograph in the Ray Society on 

 that group.... 



"Of his contributions to Botany through his sections of 

 'Coal balls' I need say nothing." 



Prof. Judd makes no reference here to the papers which 

 obtained for Williamson his F.R.S. in 1854. These embodied 

 his researches on the development of bone and teeth, in which 

 he demonstrated that the teeth are dermal appendages homo- 

 logous with the scales of fishes. This important work dated back 

 to 1842 and was inspired by his enthusiasm for the then novel 

 cell-theory of Schleiden and Schwann. 



