E. Loomis on vibrating Water-falls. 361 
and recat’ the vibration of the sheet, but with a continuous 
inward d 
n a ba of 1862, the following observations were made. 
April 18. 162 vibrations per minute. Depth of water 5 feet. 
Thermometer 44°. These vibrations were for 200 feet at north 
end of dam, alternating with vibrations in middle of dam 
April 19. Vite vibrations per minute. Depth of water 5 
feet. Therm. 
Helin 21. 136 vibrations per minute. Depth of water 5 feet. 
42°, 
April 26. pe: vibrations per minute. Depth of water 3°18 
feet. Therm 
ay 6. 160 vibrations per minute. Depth of water 3:25 
feet. Therm 
ay 6. 154 vibrations per minute. Depth of water 2°95 
feet. Therm 
April 18, 1863, Mz. Coolidge observed the number of vibra- 
tions to be 122 per minute, “and the depth of water 54 feet 
measured on the crest of the dam. 
The following table presents a summary of 
Mr. Coolidge’s observations at Lawrence, Mass. 
ae. ge tog aes ‘|| reas: wan one vibration 
2,May 62°95 feet. 08390 1861, rete 5|3°63 feet. 08-375 
1861 April 20/308 ‘875 « — April 16/500 “ “510 
o Apr isis “ 372 1862, a 18/500 “ “370 
1862, April 26/$-18. "383 z te il 19/500 “ “446 
ay 563825 “ “400 i! 215n0 “ 441 
1861, March 11 3-41 a "B75 |1863, abril 18/550 “ “492 
The first seven of these observations agree with each other 
about as well as such observations usually do. The mean of 
these seven observations gives a er of 3°23 feet, and the 
created openings in pe descending sheet of water. I have there- 
witness the vibrations with considerable force. I found it very 
ifficult to count the number of vibrations satisfactorily.. For a 
Mis eee the pulsations would be very marked, and then they 
often become so faint as to be noticed with di ifficulty, so 
that it was generally impossible to follow them for an entire 
