108 Mr. SAMUEL HUNTER, 

Fig. 9. 
A curve produced from a similarly constructed machine set at 
random is given in fig. 10. 

It is unnecessary to speak of Foucault’s process of hand abrad- 
ing or the American system of local polishers, as these require 
highly skilled artificers to be successfully used. 
The choice of machines evidently lies between that of Lord 
Rosse’s and that of Mr. Grubb’s No, 2. The latter is so compact 
and admits of such a variety in the curves which the polisher _ 
