92 H- J- Grayson: 



I am greatly indebted to Professor Orme Ma.sson, F.R.S., who as 

 President of the Professorial Board and Dean of the Faculty of 

 Science, used his influence for the promotion of the undertaking 

 and whose efforts made it possible for a proportion of my official 

 time to be given to the work. To my friend, Mr. James Fawcett, 

 of Camberwell, my heartiest thanks are due for the time and trouble 

 he bestowed upon the preparation of the plan of the machine 

 appearing as Plate VI., and for several minor drawings. Finally, 

 I am fully cognisant of the fact that I owe to the University or its 

 governing authorities, whose consideration and generosity have 

 made it possible for me to devote so much of my time to the 

 completion of this work during the past three years, far more than 

 this verbal expression of my indebtedness conveys. 



DESCRIPTION OF PLATES. 



Plate VI. — Plan of Ruling Engine. 

 ,, VII.— End view of Ruling Engine. 

 ,, VIII. — Side view of Ruling Engine — Right hand. 



IX. — Side view of Ruling Engine — Left hand. 

 ,,, X. — Front view of Ruling Engine. 



XI. — Fig. 1. Apparatus for refining crudely separated 

 abrasive. 

 Fig. 2. Apparatus for grinding the screw. 

 .,, XII. — Fig. 1. Alundum, average diameter of grains, 1-500 

 inch. 

 Fig. 2. Alundum, average diameter of grains, 1-4000 



inch. 

 Fig. 3. Carborundum, average diameter of grains, 



1-2000 inch. 

 Fig. 4. Carborundum, average diameter of grains, 



1-4000 inch. 

 Fig. 5. Emery, average diameter of grains, 1-1000 



inch. 

 Fig. 6. Emery, average diameter of grains, 1-4000 

 inch. — Figs. 1 to 6, x 75. 

 .,, XIII. — Fig. 1. Curve indicating condition of screw prior to 

 re-grinding. 

 Fig. 2. Curves showing progressive improvement 

 during re-grinding. 



