AS A VEHICLE OE SOUND. 
207 
vapour during the storm the heterogeneity thus arising was in great part abolished, and 
a freer passage opened for the sound through the atmosphere. 
To rain, finally, I have never been able to trace the slightest deadening influence upon 
sound. The reputed barrier offered by “ thick weather” to the passage of sound was 
one of the causes which tended to produce hesitation in establishing sound-signals on 
our coasts. It is to be hoped that the removal of this error may redound to the 
advantage of coming generations of seafaring men. 
§11. Action of Snow. 
Falling snow, according to Derham, offers a more serious obstacle than any other 
meteorological agent to the transmission of sound. We have not extended our obser- 
vations at the South Foreland into snowy weather ; but I may be permitted to refer to 
an observation of my own which bears directly upon this point. On Christmas night, 
1859, 1 arrived at Chamouni, through snow so deep as to obliterate the road-fences, and 
to render the labour of reaching the hamlet arduous in the extreme. On the 26th and 
27th it fell heavily. On the 27th, during a lull in the storm, I reached the Montanvert, 
sometimes breast-deep in snow. On]the 29th the entry in my journal is, “ Snow, heavy 
snow ; it must have descended through the entire night, the quantity freshly fallen is so 
great.” Dr. Derham had referred to the deadening effect produced by a coating of fresh 
fallen snow upon the ground, alleging that when the surface was glazed by freezing the 
damping of the sound disappeared. 
On December 29 1 took up a position beside the Mer de Glace, with a view to 
determine its winter motion, and sent my assistants across the glacier with instructions 
to measure the displacement of a transverse line of stakes planted previously in the snow. 
I was standing at the time beside my theodolite, having waded to the position through 
snow which, being dry, reached nearly to my breast. A storm drifted up the valley, 
darkening the air as it approached. It reached us, the snow falling more heavily than 
ever I had seen it elsewhere. It soon formed a heap on the theodolite ; still through 
the telescope I was able to pick up at intervals the retreating forms of the men. Here 
there was a combination of thick snow in the air, and of soft fresh snow on the ground 
such as Derham could hardly have enjoyed. Through such an atmosphere, however, I 
was able with my unaided voice to make my instructions audible for half a mile, while 
the experiment was rendered reciprocal by one of my assistants* making his voice 
audible to me. 
Many years ago I mentioned this fact in the presence of Sir John Herschel, and I 
have a distinct recollection of the surprise with which he heard it. And, indeed, in 
relation to our previous convictions, it is simply astonishing to observe the facility with 
which sound makes its way among obstacles, and even penetrates solid bodies, so long 
as the continuity of the air in their interstices is preserved. The following experiments 
illustrate this. 
* Mr. Joseph Taikbaz, now a photographer at Chamouni. 
