Informed awareness of barometric pressure leads to safer and more efficient navigation
Mariners Pressure Atlas
$19.95 ...item# 1995
The primary goal of this publication is to make mariners more aware of barometric pressure and how it might add to the safety and efficiency of their time on the water and to provide a specific, dependable method of storm warning in the tropics.
It is also intended to show the great value of an accurate barometer. The days of only caring about rise and fall, fast or slow, should be relegated to the history books. We now have ready access to accurate instruments and all the benefits they provide.
...in short, we have worked our way back to the 1700s when mariner's had the benefit of accurate mercury barometers for their weather analysis, and indeed learned much from them.
From the title page
“The slightest deviation from the barometric mean between the tropics demands on the part of the commander immediate attention.” — The Mercantile Marine Magazine, Vol 1, January, 1854, page 8.
At the time of that quote, mariners were using mercury barometers. Three months later in the April issue, they bring up this point again in an article that compares the then new aneroid barometers with the traditional mercury barometers. They speculate that the aneroids may not be linear over their full range and call for a careful study before the above pressure observations will be useful.
This is exactly what happened. Traditional mercury barometers were very tedious to use at sea, but they were accurate once known corrections were made. Common aneroids at the time were not, and before the Internet came about it was very difficult to calibrate an aneroid device. So the use of accurate pressure observations fell out of modern teaching (as the aneroids replaced mercury devices)—nevertheless, the proposal has been mentioned in Bowditch throughout the years. Now with good electronic barometers and convenient ways to calibrate any barometer, we can again use this valuable information for tropical storm warnings.
Sample charts below (click image to enlarge)