474 SPECIAL METHODS OF DISCOVERY. 



inventions, the spheres of our senses of tasting and smell- 

 ing ; but whether the necessary truths upon which such 

 inventions must be based have yet been discovered, would 

 be a difficult point to determine. 



The invention of new instruments not only enables us 

 to extend immensely the range of application of our senses 

 and physical powers, but is beginning also even to enlarge 

 that of our intellectual faculties. Investigation also of the 

 essential conditions and modes of action of our intellectual 

 powers, viz., memory, comparison, judgment, and inference, 

 combined with advanced knowledge of the physical sciences, 

 will probably enable us before very long to make great 

 discoveries and inventions in this particular department, 

 and to extend the range of the human intellect, in a way 

 similar to that in which we have already extended that of 

 our limbs and our senses. 1 



The following are some examples of discoveries made by 

 the use of new instruments : Torricelli invented the baro- 

 meter in 1644, and soon made by its assistance some very 

 important discoveries. He asked himself, why does water 

 rise in a vacuous tube ? and concluded that it was pressed 

 up by the weight of the atmosphere; and he inferred 

 that as mercury was nearly fourteen times as heavy as 

 water, it would rise only to about one- fourteenth part of 

 the height, and he accordingly found by experiment that 

 whilst water would rise to a height of about 34 feet, mer- 

 cury would only rise to about 30 inches. Christian 

 Huyghens, living at the same period, appears to have been 

 the first to apply pendulums to clocks. Otto-Gruericke, 

 by the invention and use of his air-pump, in 1650, con- 

 firmed the existence of atmospheric pressure. By the 

 assistance of firearms, G-assendi determined approximately 



1 Compare pp. 54-58. 



