When the cylinder r =a is moved with velocity U and r =b with velocity U 1 along Ox, = U **b e** - a,1 r +0 cos 0 - U ib2 - 2 a, (r +Q 2 ') cos 0, = - U be a2 a2 (b 2 - r) sin 0 - Uib2 b1)a, (r - ¢2 sin 0; b and similarly, with velocity components V and V 1 along Oy a 2 b2 ?= Vb,_a,(r+r) sin g -Vi b, b2 a, (r+ 2) sin 0, (17) = V b, a2 a, (b2 r) cos 0+Vi b, b, a, (r- ¢ 2) cos h; (18) and then for the resultant motion z 2zz w= (U 2 + V2)b2a a2U+Vi +b a b a2 U z Vi -(U12+V12) b2 z a2b2 Ui +VIi b 2 - a 2 U1 +Vii b 2 - a 2 z The resultant impulse of the liquid on the cylinder is given by the component, over r=a (§ 36), X =f p4 cos 0.ad0 =7rpa 2 (U b z 2 + a 2 Uib.2bz a2); (20) and over r =b Xi= fp?

The reservoir begins to fall at the end of February, and continues to do so with few and short exceptions until the end of August, and it so happens that about the end of August this dotted line, b b representing actual cumulative demand, crosses the straight line a a of uniform demand, so that the excess of demand, represented by the slope from June to September, is balanced by the deficiency of demand, represented by the flatter slope in the first five months, except as regards the small quantity **b e** near the end of February, which, not having been drawn off during January and February, must overflow before the end of February.

To avoid this loss the II% is in this case to be increased by the small quantity **b e** determined by examination of the variation of the actual from a constant demand.

In assuming a demand at the beginning of the year below the mean, resulting in an overflow equal in this case to **b e** at the end of February and increasing our reservoir to meet it, we assume also that some additional supply to that reservoir beyond the 11% of the streamflow from the driest year can be obtained from the previous year.

An ax may **b e** kept near a chopping block to make kindling.