CO. K. Wead— Millimeter Screw. 177 
oo REF cAmeb 08 Oni. ie 1c metde. vane nB-08x 898T 200 
48x73 
threads. This requires two gears with a prime number of 
teeth. 
e. 
The method is based on the fact that 1 inch equals very 
nearly 25-4 millimeters; it would equal it exactly— 
If one meter equals 39°37008 inches. 
Clarke’s value “ 39°37043 “ 
Kater’s “ eo SPST Te. 
This “ mechanical” meter differs from the best determination 
yet made, Clarke’s, by no more than that differs from the next 
est one, viz: zzq/o9q part, though in the opposite direction. 
The form in which the direction was given to Buff & Berger 
was, “gear the lathe so as to’ cut a screw with twenty threads 
to the inch, with a gear of 100 teeth on the feed-screw ; replace 
the 100 by 127 (=>), and the pitch will be 1 millimeter, 
the theoretical error being much less than the mechanical error 
of cutting.” Thus, on the lathe above referred to, ay x4= 
; 12 
25'4 to the inch, or 1 to the millimeter; again, wa oi xde 
Physical Laboratory, University of Michigan, Dec. 15, 1881. 
