John Robinson

“ We therefore feel fully authorized to assert that we have frequently made voyages from America without the above articles, and we are fully persuaded that every seaman with common nautical knowledge can do the same.”
No doubt many valuable data lie hidden in old log-books and sea journals, early newspaper files, shipping records of old business houses and elsewhere. To anyone with time and the inclination for research a fascinating field is open where material of historical and scientific value may be found. ”

“ In Peabody Museum, Salem.
The early Hadley quadrants were huge affairs made of wood with an arm twenty-four inches in length. Today they are more generally of metal with arms from ten to twelve inches. Using the sextent or Hadley quadrant the observer stands facing the sun, but old Hadley quadrants were made with a “back sight” so that they could be used like the Davis quadrant, thus making two independent observations the average of which would ensure greater accuracy. ”

“ By the principle of reflection, however, it covers ninety degrees and the scale [Pg 7] is so marked. The Davis quadrant with its two arcs does represent one fourth of the circle and for that instrument the name is correct.
The Hadley was a great improvement over the Davis quadrant and other older devices for finding latitude. By moving the arm the sun is reflected by the mirror at the apex and “brought down” to the horizon line and the eye is protected by colored glasses of various degrees of density through which the sun’s rays shine. ”

“ To prevent corrosion, the scale, which is minutely divided, and has a “vernier” with a magnifying glass to show divisions of minutes, is made of gold or platinum in the best instruments. A half-circle has been devised and is exceedingly rare. An example in the Salem collection was made before 1818. ”

“ With these difficulties observations were, of course, far from accurate, but approximate time and latitude could be obtained. Another device was the ring-dial, or universal ring-dial as the old works on navigation called it. This differed from the astrolabe by having adjustable rings with the hours and scales engraved upon them. Both of these instruments are now rare.
No original cross-staff is known to the writer in any collection in this country. ”

“ It was taken from a British prize vessel off the coast of Ireland, in 1779, by Capt. James Barr in his Salem privateer. Another glass of similar form, but longer and with a mahogany case, was used on a United States naval vessel about 1815. The spy-glass, familiar to everyone, in two or three sections, was used at sea through the first half of the nineteenth century and is often seen tucked under the left arm, in the portraits of ship-masters brought home from foreign ports. Many of these were excellent instruments, especially those from Dollond of London. ”