1793* ^'^ the study of natural history. 313 



first thought of being applied to navigation by 

 placing it on a pivot *. 



The art of printing, that choice hlefsing to society^ 

 was discovered by a goldsnnith's ftiopman, trying 

 experiments with stamping with (hoe black, on wet 

 paper from some of his master's puncheons. The 

 weather glafs was discovered by Torricelii, in trying 

 various experiments with quicksilver, and paying^ 

 constant attention to the procefses and results. 



So dull and foolijh do we become by inattention, or 

 by always digging towards the bottom of a pit in 

 search of truth, v«'hen it is to be found on the sur- 

 face, that it is not even a long time since we con- 

 sidered that the only way to prevent interference 

 of pafsengers, horsemen, or carriages, on a road, is 

 for each to keep the right hard side of the road. 



You have frequently remarked, and perhaps ad- 

 mired, the volubility and lustre of the little glo- 

 bules of rain, that lie upon the leaves of kail or 

 colewort, and of other vegetables ; but I dare say 



* VVHien a highly poliflied needle is made to swim on water, it docs 

 not touch the water, but forms around it, by a repulsive power, a bed 

 whose concavity is much larger than the bulk of the needle. This 

 affords a much better explanation of the fact than the common one 

 deduced from the tenacity of the water : for the needle swimming 

 upon a fluid much lighter than itself, must needs displace a quantity oi 

 water equal to its own specific gravity ; and the repulsive power on 

 the surface occasions the singular circumstance. This instaiice leads 

 us to a just and necefsary precision in the hydiostatical law, " 'I'liat 

 the whole swimming body is equal in weight to a quantity of the fluid 

 whose bulk is equal to that of the part immersed. For it fliould be 

 exprefsed, " That the weight of the swimming body is equal to the 

 weight of the quantity of the fluid difplnccd by il. 



VOL. xvi. R R f 



