Preface ix 



to apparatus and a better condition of that already in use 

 should transpire. 



No directions are given for the adjustment of specific 

 instruments; attention has rather been paid to the acquire- 

 ment of skill in handling tools, and to the attainment of a 

 knowledge of the principles of construction, as with these 

 assets any ordinary teacher should be able to discover the 

 " fault " and amend it. 



I have to thank my friend and assistant Mr. James A. 

 Wightman for valuable help both in the text and in the work 

 of seeing the volume through the press. Acknowledgments 

 are also due to Messrs. Woolley, of Manchester, Herr Julius 

 Springer, of Berlin, and Messrs. Longmans, Green & Co., 

 from whose publications some of the figures and tables in 

 Appendix III. are quoted. 



G. H. W. 



PORTADOWN, 



April, 1908. 



