SCIENCE OF COMMON,, THINGS. t 101 



Torricelli. 



Why water rises 1& a p'lrip* 



raised, is not very considerable, as in the case where 

 the foundations of docks, &c., are to be drained. 



645 Who first ascertained and demonstrated the reason for the ascent 

 of water in a tube by suction, and in the common pump ? 



Torricelli, a pupil of Galileo. 



646 How was he led to his conclusions ? 



He argued, that whatever be the cause which sus- 

 tained a column of water in a common pump, the mea- 

 sure of the power thus manifested must be the weight 

 of the column of water ; and consequently, if another 

 liquid be used, heavier or lighter, bulk for bulk, than 

 water, then the same force must sustain a lesser or 

 greater column of such liquid. By using a much 

 heavier liquid, the 

 column sustained 

 would necessarily be 

 much shorter, and 

 the experiment in 

 every way more 

 manageable. 



Torricelli verified his con- 

 clusions in the following 

 manner : He selected for 

 his experiment mercury, 

 the heaviest known liquid. 

 As this is 13 times heavier 

 than water, bulk for bulk, 

 it followed that, if the force 

 imputed to a vacuum could 

 sustain 33 feet of water, it 

 would necessarily sustain 

 13 times less, or about 30 

 inches, of mercury. Torri- 

 celli therefore made the fol- 

 lowing experiment, which 

 has since become memo- 

 rable in the history of 

 science : 



He procured a glass tube 

 (Fig. 26) more than 30 

 inches long, open at one 

 end, and closed at tho 

 other. Filling this tube 

 with meccun r , and appl}'- 

 ing his finger to the open Kg. 2. 



