On the Motion of Water-Wheels. | 129 
cutter; the process of hardening in air is applied by artists 
to the hardening of very small drills. 
New Lebanon, Aug. 8, 18235. . 
Art. XVI.—On the motion of water-wheels—extract of a let- 
ter from Prof. CLeaveLaNp, to the editor, dated Bruns- 
wick, May 30, 1825. 
My Dear Sir, 
In a former letter, I mentioned the opinion existing in 
this part of the country, that saw-mills move faster during 
the night than the day. The explanation usually given by 
the workmen is that the air becomes heavier after sunset. 
I seleeted a fine day in August, and requested that all the 
mill-gates might remain stationary for twelve hours. At 2 
o’clock P. M. I suspended a Barometer in the mill; the 
pressure of the atmosphere was equal to 30.19 inches; the 
temperature of the water just before it passed the mill-gate 
was 72° Fahr.—The log was then detached from the saw, 
and the number of revolutions of the wheel, being repeatedly 
counted by different persons, was 96 ina minute. At mid- 
night, I again visited the same mill. ‘The Barometer stood 
at 30.26 inches, the pressure of the atmosphere having in- 
creased seven hundredths of an inch. The temperature of 
the water was 72°, the same as at the preceding observation, 
although it had been a little higher during the afternoon.— 
The log being detached, as before, the wheel was found to 
revolve precisely 96 times in a minute, showing the same ve- 
locity as at the preceding noon. ‘Fhe depth of the water 
was the same during both experiments. The workmen were 
satisfied that the result of the experiment was correct; but 
still they seemed to believe that it would be different in a 
cloudy night. 
VoL. X.—No. 1. 17 
