420 



Popular Science Monthly 



with the feet. The blind person, no matter how 

 familiar with the ground, is completely at a loss 

 when he attempts to walk in the snow, which is 

 often called 'the blind man's fog.' Somehow the 

 soft cushion of flakes destroys the tactile impressions 

 or blurs them to such an extent that the muscle 

 memory is nullified. 



"Combined with the muscle memory is an acute 

 sense of direction which the blind develop. When 

 the boys went 

 swimming in 

 the creek they 

 shed their 

 clothing seem- 

 ingly at hap- 

 hazard on the 

 banks. But on 

 coming out 

 each boy went 

 unerringly to 

 his own cloth- 

 ing, guided by 

 their sensitive 

 soles." 



The track 

 and field 

 events at 

 Overbrook 

 prove that 

 there are 

 expert ath- 

 letes among 

 the blind 

 also. 



Under professional instruction the blind boys became expert 

 swimmers and divers. Life preservers are obnoxious to them 



The Liberty Bell Is Sick and That 

 Is Why It Cracked 



METALS have diseases and lose their 

 vitality. They become tired or 

 fatigued, just like human beings, and are 

 weakened as a consequence. That is what ails 

 the old Liberty Bell, resting in Independ- 

 ence Hall, Philadelphia, Pa 



To understand this, a littk 

 of the bell's history is neces 

 sary. Cast in London, Eng- 

 land, by Thomas A. Lester, 

 it arrived in Philadelphia 

 in 1752 and was tested in 

 August of the same year. 

 It was cracked at once 

 by the clapper's stroke. 

 Instead of returning 

 the bell to England, it 

 was remelted and cast 

 again, but ten per cent 

 extra copper was added 

 to it. This seemed to 

 spoil its sound. It was 

 remelted and cast a third 

 time. Tin was added to 

 restore the sound . 



The actual quantity of 



The first crack extends about two 

 thirds of the distance from lip to top. 

 The second is shown by the dotted lines 



the various metals used is not known, but 

 it is certain that to melt and handle the 

 two thousand pounds necessary at least two 

 dozen of the largest eighteenth century 

 crucibles or melting pots were required. 

 Evidently the bell could not have been 

 uniform throughout. It did not cool evenly, 



and so, 

 what are 

 known as 

 shrinkage 

 strains were 

 set up. It is 

 just as if 

 enormously 

 powerful 

 hands were 

 constantly 

 trying to 

 tear the 

 metal like so 

 much paper. 

 As a result, 

 the first 

 large crack 

 which is . so 

 prominent 

 to-day ap- 

 peared. 



One dis- 

 ease of met- 

 als is due to too much remelting. It seems 

 that their life is destroyed, their real value 

 burned out of them. Tests made in re- 

 melting copper several times under the best 

 conditions have shown that with each melt- 

 ing the metal loses largely in tensile strength 

 and springiness. Bending tests show a loss 

 of over fifty per cent from 

 three meltings. The Liberty 

 Bell was recast three times. 

 Tin is also known to be 

 often afiflicted with the 

 "tin pest." Particularly 

 in a cold climate does it 

 seem to finally turn gray 

 and crumble. Organ 

 pipes in a church in 

 Lietz, Prussian Sax- 

 ony, Germany, decay- 

 ed in 1 85 1. They 

 were afiflicted with the 

 tin pest. There is tin in 

 the Liberty Bell, too. 



Our sacred national relic 

 has probably had more 

 trips over the country to 

 various fairs and exhibi- 

 tions than any other in 



