TRANSACTIONS OF SECTION A. 443 
1 9 9 9 7 
= —________| —(1 — 2k?) 2p? |cos P22 cos 22. E Fd 
(p+1) aoe J 
+ 2(p-1) (p—2) - @p*—8p + By} [cost cos 20. EFA 
+ {4(p-2) — (2p - 7)h*} 
d 
[cosP—4, BFde + 4 |cos UREN Mi 
+ 4n°|sin x cosa cos 2. FAdx + (A? F'+ F)2 cos?-? cos 22. 
~—{(1—#? — pA?) cos 2a —(1 + cos? x)A7}2 sin x cos EF | 7 Vile 
i! Oye 2° Dr I—2,, a Da J2 - 
Sas | —{p--2(p+ lk }2p cos! uv cos 20,H7da 
+ {2(p—1) (p—2)—(2p?—8p + yk} | cos?—4z cos 2a. 7da: 
feos cos 22. E7*dx = 
+ {4(p—2) -—(2p-1) 2} |cos?—tr.B°de 
= 4) cos? cos 2v.Atdx + 4A2EF cos?-2x cos 2a 
—[8{(1—2°) - pa} cos 22° +(1—8 cos? x) A®] sin x cos? tr. | VII. 
8. On the probable Explanation of the Effect of Oil in Calming Waves 
ma Storm. By HE. P. Cunverwext. 
When the surface of the sea has become quite smooth after a storm, it is very 
common for long rollers to break on a sand bar. If there be no wind and the sea 
be glassy, these will not break until quite close to the shore, even though the ordi- 
nary theory points to their breaking earlier, unless a force directed in the opposite 
direction to that of their motion be exerted on the wave. Such a force might be 
supplied by the wind ; but if it rise in any direction the waves break much sooner. 
This effect is therefore due to some secondary effect produced by the wind’s pres- 
sure, and not directly by the pressure itself: and it is to the ripples produced on 
the surface (which disturb the wave motion), that the speedy breaking is to be 
attributed. It is, however, a direct result of theory that the ripples depend on 
surface tension for their propagation, and cannot exist in large amount on the oiled 
surface. It is also evident that the hold of the wind on the wave is greatly de- 
ereased by the absence of ripples, and thus the oil acts both to prevent the wind 
haying much effect on the surface, and also to prevent the motion of the water in 
the wave itself being such as to cause breaking. The amount of friction may per- 
haps sensibly influence the breaking, but definite experiments on this are still 
wanting. i 
9. On the Pressure of the Vapour of Mercury at the Ordinary Temperature. 
By Professor McLeop, F.R.S. 
At the last meeting of the Association Lord Rayleigh called attention to a paper 
_ that had appeared in the ‘Annalen der Physik und Chemie’ (N. F. xvi. 610), by 
Hagen, on the Pressure of Saturated Mercury Vapour at Low Temperatures. The 
pressures given for the ordinary atmospheric temperatures, although considerably 
less than those published by Regnault, appeared rather higher than some recent 
observations seemed to warrant. 
A method of determining the vapour pressure at ordinary temperatures seems to 
have occurred to Mr. Crookes and the author almost simultaneously, and he much 
regrets that the absence of the former from the present meeting prevents the Asso- 
ciation learning the results of his work. Mr. Crookes intended to try the experi- 
ment in vacuo, whereas the author thought of saturating air with mercury vapour ; 
but both intended to determine the quantity of evaporated mercury by a chemical 
test. 
