Ng 104 On the Acceleration of Water WA, 
Art. XIX.— On the ee iicitapaeai of the ‘edtion of 
Water Wheels during then night and i in winter. 
1. Extract of a letter from Tuomas Krspatt, Jn. to the 
= Editor. 
New-Lebanon, Sept. 28, 1824. 
“ Dear Sin, | 
Iv compliance with a wish Peiiteaict ina vedi if the 
last Journal, respecting the different velocity of water 
mills by day ‘and by night, I would observe that the fact is 
well known to those who are conversant with water works. 
It is: more sensibly discovered in the spinning of cotton, 
than in most other kinds of business, as it is the general 
practice to run the machinery as fast as it can be well at- 
_ tended, and it becomes necessary to lower the gate and 
let on les s water in the evening than in the day time; the 
the hum of the mill is very sensible t 
8 oe iti is the case, in aft temperatures and all 
some years since J have been in a situa- 
ea rvations, and cannot probably be ed 
‘facts which were observed at the time. When 
noticed the fact in question, I enquired of the olds 
mill workmen as to the cause, and was told that water was 
heavier in the night than in the day time, and supposed at 
the time that it was occasioned by a difference in the at- 
mospheric pressure, and pushed my inquiries no farther. 
The mills in which the different velocities were noticed 
were of the horizontal or tub wheel construction. I do not 
recollect to have noticed it in a mill where a breast wheel 
was used, although { had opportunity to observe the e latter, 
but probably the fact being familiar, had ceased to excite 
my attention, and was supposed to be the same as in the 
case of horizontal wheels. As it respects ‘‘ mills movin 
more slowly as the water approaches the freezing point,” 
will relate a circumstance which I never knew or heard of 
at any othertime. It occured at a mill owned by Messrs. 
‘Trowbridge, Merrifield, & Wilson, in Worcester, Mass., 
