468 Scientific Intelligence, 8?c. 



willow trees grow near the mansion ; under their shade he often 

 enjoyed the summer evening breeze. 



" His laboratory is now converted into a house for garden-tools ! 

 the furnaces pulled down! the shelves unoccupied! — the floor co- 

 vered with Indian corn ! A stranger might be inclined to say, 



" Sic transit gloria philosopbia?.'' 



" But, when the chemist, or the historian, or the philosopher, 

 or the divine, examine the records of the various branches of 

 learning in which they are skilled, then will his name be honoured. 

 To this laboratory the children from the school were accustomed 

 to come, once a week, and he would amuse them with experi- 

 ments. 



" The tomb of my grandfather, Dr. Priestley, is in the environs 

 of the town, surrounded by a low wall. I knelt by my ancestor's 

 tomb, and the perils of my pilgrimage were remembered with plea- 

 sure." 



Article XI. 



SCIENTIFIC INTELLIGENCE, &C. 



I. — Plumbago and Black Lead Pencils. 



There is only one purpose to which this form of carbon, is applied 

 in the solid state, viz., for the manufacture of black lead pencils, 

 and its adaptation to this end depends upon its softness. In the 

 state of a powder, plumbago is used to relieve friction. Its power 

 in this way may be illustrated by rubbing a button first on a plain 

 board, five or six times, and applying it to a bit of phosphorus, the 

 latter will immediately burn. When rubbed on a surface covered 

 with plumbago, double or triple the friction will be required to 

 produce the same effect. One of the most remarkable circumstances 

 connected with plumbago is the mode in which it is sold. Once a year 

 the mine at Borrowdale is opened, and a sufficient quantity of plum- 

 bago is extracted, to supply the market during the ensuing year. It is 

 then closed up, and the product is carried in small fragments of 

 about three or four inches long, to London, where it is exposed to 

 sale, at the black lead market, which is beld on the first Monday 

 of every month, at a public-house in Essex-street, Strand. The buy- 

 ers, who amount to about seven oreight, examine every piece with a 

 sharp instrument, to ascertain its hardness — those which are too soft 

 being rejected. The individual who has the first choice pays 45s. 

 per pound ; the others 30s. But as there is no addition made to 

 the first quantity in the market, during the course of the year, the 

 residual portions are examined over and over again, until they are 

 exhausted. The annual amount of sale is about £3000. There 

 are three kinds of pencils, common, ever-pointed, and plummets. — 

 The latter are composed of one-third sulphuret of antimony and 

 two-thirds plumbago. 



