261 Mr Sang's Aimnal Report on the 



We should then have expected all the recent improvements 

 in exact workmanship to have emanated from the laboratory 

 of the philosopher. But such has not been the case. The 

 improvements in the art of turning, for instance, have almost all 

 of them had reference, not to the turning of the axis of an 

 astronomical circle, or to the perfect elaboration of its limb ; but 

 to the vulgar and common-place matters of constructing a sugar- 

 roller, or of fitthig steam-tight the cover of a cylinder ; and 

 while the slide-rest and self-acting lathe are tools indispensable in 

 the machine-shop, they are but beginning to assert their right to 

 enter the shop of the philosophical instrument-maker. The exac- 

 titude of fitting exhibited in a common spinning-frame, or in a self- 

 acting mule, equals, if it do not surpass, that which is attained 

 even in our superior theodolites and circles ; and the most 

 beautiful of our air-pump fittings vanish before the exquisite 

 adaptation of our steam-engines. 



This inversion of the relative positions of tool-making and 

 instrument-making, must attract the attention of every one who 

 is conversant with the tools used, and methods followed by the 

 two classes of workmen ; and becomes particularly conspicuous 

 when we enter the larger and more recent of the tool manufac- 

 tories. There we find planing-engines, and lathes of enormous 

 dimensions, the finish and workmanship of which would honour 

 our best observatories, pursuing silently, and almost unattended, 

 their laborious avocations; cutting down material till its surface 

 rival in smoothness and finish the parts of the machines them- 

 selves ; we find them stopping, and reversing, and renewing 

 their actions, with such composure and sagacity, that one is al- 

 most tempted to investigate the position of their sensorium. 



In this paper I propose to lay before the Society a short and 

 general account of what seem to me the latest and most remark- 

 able improvements in these two instruments, the Planing-en- 

 glne and Turning-lathe. 



The parts of all machines are made to move upon each other ; 

 now, it is well known to the geometer, that there are only three 

 kinds of lines which possess the property of gliding along their 

 counterparts ; these are, the straight line, the circumference of 

 the circle, and the helical spiral. 



