In their newsletter "Detroit Marine Historian," the Marine Historical Society of Detroit runs an excellent series of marine news from 100 years ago. The news is excerpted from various Great Lakes-area newspapers in the Historical Collection of the Great Lakes at Bowling Green. The newsletter is well worth the cost of membership, and you get a great calendar.
On October 10, 1910 the Toledo Blade reported, "At what is known as the southeast shoal in Lake Erie, the Canadian government has stationed the lightship Balken, with a submarine bell and orders have been issued for the bell to be rung every every day during the present month... Most of the vessels of the lakes are now equipped with apparatus for receiving the signals of the submarine bell, and as the signals can be sent a distance of 10 miles, the constant ringing of the bell will aid many a ship in that vicinity during a storm or a heavy fog to keep clear of the dangerous shoals. The submarine bell is lowered to a depth of about 20 feet and is kept ringing continuously by means of compressed air. No matter how hard the wind blows across the lakes, the signals of the submarine bell will be carried beneath the water in every direction."
I was familiar with wireless telegraphy as an advance in marine safety, but confess I had never heard of the submarine bell. I looked for more information and found this article:
http://www.uscglightshipsailors.org/library/sub_bells/
I still don't understand exactly how they worked. Was the bell actually in the water, or was it in an air chamber beneath the surface? It seems to me that the water would muffle the bell. Can anyone recommend a good book about lightships? The more I learn, the more I find out how much I don't know!