356 E. Loomis on vibrating Water-falls. 
and on the crest, by comparing it with the top line of the abut- 
ment, which appeared to have been levelled with considerable . 
care. In this manner it was found that when the depth, as shown 
by the gauge, was 974 inches, the depth on the crest was 15 
inches less. The following table exhibits the average of a con- 
siderable number of comparisons. 
| Depth by gauge. | Depth on crest. } Difference. 
14°75 inches. 12°25 inches. 2°5 inches, 
16°5 “ 138°5 “ 3 “ 
23 “ 19 . eer 
975 825 . 15 eS 
For depths less than two feet, the depression of water on the 
crest of the dam is 0°175 of the depth by the gauge; but for a 
depth of 8 féet, the depression is 0°154 of the depth by the 
gauge. From these results, I have deduced the depth of water 
e 4 ft. 52 in. 
April 13th, toward evening, the vibrations were very strong 
for 6 or 8 times, then feeble for about as many m 
ore; and soon. 
alternately strong and feeble. Near the middle of the sheet, the - 
vibrations were tolerably regular; but towards either extremity, 
d 
it appeared inclined to stop, and seemed to be forced into vibra : 
en by the power of the middle portion of the sheet. 
aed 
Pe 
Th 
ft. 94 in. - 
April 14th, 1861, the vibrations had ceased entirely. Gauge _ 
it. 8 inches. 
1 15th, the sheet of water was extremely smooth, without - 
itest sign of vibrations. Through the passage way in 
