104 On the Acceleration of Water Wheels, 



Art. XIX. — On the asserted acceleration of the motion of 

 Water Wheels during the night and in winter, 



I. Extract of a letter from Thomas Kendall, Jr. to the 



Editor, 



Mw-Lebano7i, Sept. S13, IQ^i. 

 " Dear Sir, 



In compliance with a wish expressed in a remark in 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 less water in the evening than in the day time; the 

 difference in the hum of the mill is very sensible to a by- 

 stander. 



I cannot say that it is the case, in all temperatures and all 

 weather, as it is some years since I have been in a situa- 

 tion to make observations, and cannot probably remember 

 all the facts which were observed at the time. When I 

 first noticed the fact in question, I enquired of the older 

 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 I had opportunity to observe the 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 moving 

 more slowly as the water approaches the freezing point," I 

 will relate a circumstance which I never knew or heard of 

 at any other time. It occured at a mill owned by Messrs. 

 Trowbridge, Merrifield, & Wilson, in Worcester, Mass., 



