Over a concentric cylinder, external or internal, of radius r=b, 4,'=4,+ Uly =[U I - + **Ui**]y, (4) and 4" is zero if U 1 /U = (a 2 - b2)/b 2; (5) so that the cylinder may swim for an instant in the liq**ui**d without distortion, with this velocity **Ui**; and w in (I) will give the liq**ui**d motion in the interspace between the fixed cylinder r =a and the concentric cylinder r=b, moving with velocity U1.

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 - **Ui**b2 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 liq**ui**d 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 **Ui**b.2bz a2); (20) and over r =b Xi= fp?

The calculation of the expressions in brackets may be simplified by taking the pairs in terms from the outside; by finding the successive differences of uo + um, ill + um_l, ..., or of **uI** u i +umi, ..

It was at this stage that the language spread in Lahul and Spiti, where the superscribed letters were silent, the d and g finals were hardly heard, and as, os, us were ai, oi, **ui**.

The vowel sounds ai, oi, **ui** have become e, o, u; and a, o, u before the finals d and n are now et, o, ii.