AS A VEHICLE OF SOUND. 
205 
Formic ether. — Action decided, but weak. 
Alcohol. — No sensible action. A more delicate test is necessary*. 
Acetic ether. — Action decided, but weak. 
Nitrite of amyl. — Action uncertain. 
Toluol. — No sensible action. 
Valerianic ether. — No sensible action. 
Butyric ether. — No sensible action. 
Acetone. — Action very weak. 
When the flasks containing iodide of ethyl, formic ether, and acetone were placed in 
warm water, their vapours exerted a strong action. The warming of valerianic ether, 
butyric ether, and alcohol, on the contrary, produced no sensible effect. 
In all cases where an action was observable, the air-bags used to force air downwards 
might be suppressed, the saturated air only being forced across the tunnel ; the result 
was the same as when common air was forced from bags in a direction opposed to that 
of the saturated air. 
The action of non-homogeneous atmospheres is well shown by placing a ticking watch 
at 6 inches from the ear. The heated air-column from a Bunsen’s rose-burner utterly 
stops the sound. I may add that all these results may be obtained with an apparatus 
only a fraction of the length of that first employed, and figured on Plate XVIII. 
§ 10. Action of Hail and Bain . 
The explanation here given is in harmony with other facts, while these facts are 
irreconcilable with prevalent notions. Dekham, and after him all other writers, con- 
sidered that falling rain tended powerfully to obstruct sound. I have already referred 
to an observation on June 3 which tended to throw doubt on this conclusion. Two 
other crucial instances will suffice to show its untenability. On the morning of Oc- 
tober 8, at 7.45 A.M., a thunderstorm accompanied by heavy rain broke over Dover. 
But the clouds subsequently cleared away and the sun shone strongly on the sea. For a 
time the optical clearness of the atmosphere was extraordinary, the coast of France, the 
Grisnez lighthouse, and the Monument and Cathedral of Boulogne being clearly visible 
in positions from which they were generally quite hidden. The atmosphere at the same 
time was acoustically opaque. At 2.30 p.m. a densely black scowl again overspread the 
heavens to the W.S.W. At this hour, the distance being 6 miles, the horn was heard 
very feebly, the syren more distinctly. The howitzer was better than either, though not 
much superior to the syren. All was hushed on board during these observations. 
A squall now approached us from the west. In the Alps or elsewhere I have rarely 
seen the heavens blacker. Vast cumuli floated in the N.E. and S.E. ; vast streamers of 
rain were seen descending W.N. W. ; huge scrolls of cloud to the N. ; but spaces of blue 
were to be seen to the N.N.E. 
* While this paper was passing through the press the action both of aqueous vapour and of the vapour of 
alcohol mixed with air upon sound was experimentally demonstrated. 
