6o GREAT MEN OF SCIENCE 



was hung up by a thread in a glass vessel which could be 

 evacuated; the sound of the bell ceased to be heard after the 

 air had been sufficiently pumped out. But noises were 

 frequently observed to escape from a vacuum, which some- 

 what confused Guericke; he appears, since these experiments 

 were not continued sufficiently, to have been deceived by the 

 conduction of sound through solid bodies. 



The burning of a candle, and the life of animals, failed 

 already in a space from which the air had been only partially 

 removed, and Guericke immediately drew the conclusions 

 that fire takes up something from the air which it needs to 

 maintain itself, and hence that it consumes air; a fact, by the 

 way, also stated by Leonardo. He followed this up in special 

 experiments, using a quantity of air enclosed over water, and 

 found that a burning candle used up at least one-tenth of 

 the air before it went out. 



A large number of experiments were made by Guericke 

 with very expensive apparatus, not so much for the sake of 

 the investigation itself, but rather in order to produce an 

 effect on his contemporaries with what he had discovered. 

 In this category are arrangements which caused great force 

 to be exerted, for example a very large copper cylinder with 

 pistons, which, when suddenly connected with a space 

 previously evacuated, was able to overthrow twenty, thirty, 

 or even fifty men, who were pulling on the pistons by ropes. 

 The effective force is given by Guericke from the air pressure 

 as calculated by him ( a water column of twenty Magdeburg 

 ells or ten metres) correctly in pounds; but he also tested it by 

 weights on a balance, and states how one can easily calculate 

 the total weight of the air on the earth, if we know the total 

 surface of the earth. 



The best known of these arrangements was the 'Magde- 

 burg hemispheres,' the smaller of which, having a diameter 

 of three-quarters of a Magdeburg ell, could only with 

 difficulty be separated by a team of eight horses on either side. 



