232 
PROFESSOR TYNDALL ON THE ATMOSPHERE 
time to time taken part in the inquiry. To the eminent arctic navigator Admiral 
Collinson, who showed throughout unflagging and, I would add, philosophic interest in 
the investigation, I am indebted for most important practical aid: he was almost 
always at my side, comparing opinions with me, placing the steamer in the required 
positions, and making with consummate skill and promptness the necessary sextant 
observations. I am also deeply sensible of the important services rendered by Mr. Dou- 
glass, the able and indefatigable Engineer, of Mr. Ayres, the Assistant Engineer, and 
of Mr. Price Edwards, the Private Secretary of the Deputy Master of the Trinity House. 
The officers and gunners at the South Foreland also merit my best thanks, as also 
Mr. Holmes and Mr. Laidlaw, who had charge of the trumpets, whistles, and syren. 
In the subsequent experimental treatment of the subject I have been most ably aided 
by my excellent assistant, Mr. John Cottrell. 
Appendix. 
On Gun-flashes as Fog-signals. 
In crossing to Ireland to witness experiments instituted by the Board of Irish Lights, I have usually ques- 
tioned the intelligent and courteous captains of the steamers plying between Holyhead and Kingstown regarding 
the coast-signals. I was distinctly informed by some of them that in fogs so thick as entirely to quench the 
powerful revolving light of the South Stack, the flash, or rather the glare upon the fog, produced by the gun at 
the North Stack was usually visible and of great utility. Bearing upon this remarkable point I have been 
favoured with the following letter from Captain Galway, which seems well worthy of insertion here : — 
“ November 27, 1873. 
“Dear Sir, — Mr. Wigham having communicated to me a wish expressed by you to have an account of an 
observation of mine with respect to the fog-gun on Lundy Island, in the Bristol Channel, I have much pleasure 
in forwarding you a detailed account of the circumstance, and beg to say that I feel gratified that you should 
think the observation worthy of your notice. I was on board the Bristol Steam Navigation Company’s steamer 
‘ Inverna,’ on a passage from Waterford to Bristol, on Sept. 9 last. We left Waterford at 8 a.m., and at 11.10 
a.m. were abreast of the ‘ Conningbed ’ light-ship. When we took our departure and shaped a course S.E. by 
S. I S. to pass a short way to the westward of the Smalls, or failing seeing them (the weather being thick) to 
make Lundy Island, we put the patent log over at the same time. The weather was thick, wind W.S.W., with 
drizzling rain. At 3 p.m. we were keeping a look-out for the Smalls lighthouse, but were unable to see it owing 
to the thickness of the weather. At 8 p.m., estimating that we had run our distance, we hauled in the patent 
log and found that it registered 84 miles, the distance being 90 miles. We therefore thought we must be near 
Lundy Island, and were peering into the fog, looking out anxiously for the light. I suggested to the captain 
that he should keep away a little up the Channel in order to bring the gun more to windward. This we did? 
and about ten minutes afterwards we observed a flash as that of a gun bearing about south. I noted the time, 
8.15 p.m., G.M.T., and remarked that I thought it must be the gun on Lundy, but could not understand our 
not being able to see the light. The weather at the time was thick, occasionally clearing and then thickening 
over again, with light showers of rain quite obscuring the horizon. I had remarked to the captain just before 
that I did not think he could see a first-class light for more than a mile. I watched the time, as I was not 
sure of the intervals at which the gun was fired and had no Admiralty List of Lights on board, and the chart 
the captain had did not give the required information. I felt certain, however, that it was either fifteen or 
seventeen minutes ; and at 8.31 p.m. I again observed the flash : this time I was satisfied that I heard a slight 
concussion, but I am sure I should not have perceived it had not my attention been riveted to the spot by the 
flash. The vessel was also more to leeward of the gun and the engines stopped. At 8.45 I again saw the flash • 
distinctly and caught a slight reverberation, and a few minutes afterwards (the fog lifting a little) we observed 
