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Updated: June 13, 2025
He found that, while the radiating power of clean lead was only 19, it rose to 45 when tarnished by oxidation, that the radiating power of plumbago was 75, and that of red lead 80. He also discovered that, while the radiating power of gold, silver, and polished tin was only 12, that of paper was 98, and lamp black no less than 100.
John and the Borrowdale mountains. BUTTERMERE stands near the foot of the lake, and by Seatoller is fourteen miles from Keswick. Taking the vale of Newlands by the way, the distance is much less. In the vicinity of Seatoller is the celebrated mine of plumbago, or black lead.
Signor Garibaldi is a retired wine merchant driven out-of-doors by illness, a most courteous and sensitive soul, with a talent for letter-writing that is alone worth all the plumbago blossoms that he cut away last year.
The boats having been gently and carefully lowered into the water without a splash, or so much as a single tell-tale squeak from the tackle-blocks the pins and bushes of which were habitually overhauled at frequent intervals and kept well lubricated with a mixture of melted tallow and plumbago the crews took their places, each man carefully depositing his drawn cutlass on the bottom-boards between his feet, and we shoved off with muffled oars, the three boats pulling abreast, with about a ship's length between each; so that if perchance we should happen to be seen, we should present as small a target as possible to aim at.
To the Woolsey boys, holding and steadying the old man, the cañon had never seemed so deep. At last they reached the Plumbago Mine, on the opposite height, where they borrowed two mules to carry them the rest of the way. It was easy going now as far as Chipp's Flat.
In 1873, or thereabout, he claimed to have observed, while constructing rheostats, or electrical resistances for making an artificial telegraph line, that powdered plumbago and carbon has the property of varying in its resistance to the passage of the current when under pressure. The variation seemed in a manner proportional to the pressure.
It consisted of an electro-magnet with double poles and an armature which pressed upon a disc or discs of plumbago, through which the local current Passed. The electro-magnet was excited by the main line current and the armature attracted to its poles at every signal, thus pressing on the plumbago, and by reducing its resistance varying the current in the local circuit.
At the cataracts of the great rivers Orinoco, Nile, and Congo, the syenitic rocks are coated by a black substance, appearing as if they had been polished with plumbago. The layer is of extreme thinness; and on analysis by Berzelius it was found to consist of the oxides of manganese and iron.
In later years we became good friends, and he did not hesitate to give credit and even to advance considerable sums. My sketches from Breuil were made under difficulties; my materials had been carried off, nothing better than fine sugar-paper could be obtained, and the pencils seemed to contain more silica than plumbago. However, they were made, and the pass was again crossed, this time alone.
This may mean the making of an exact impression of a medal, coin, or other figure, or a depositing of a coating of the same on any metallic surface. Formerly the faces of the types used in printing were very commonly faced with copper to give them finish and a wearing quality. Even fresh, natural fruits that have been evenly coated with plumbago may be covered with a thin shell of metal.
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