Photo from Bureau of Standards 



the; most powerful magnet in the world 



This magnet is so powerful that it will draw nails resting on the palm of a hand from 

 a considerable distance; or, if the nail is placed in the closed fist, the attraction of the magnet 

 is so great that the hand can be turned with only great effort. The magnet is used to study 

 the strange effect of magnetism on light waves. 



ances are so delicate that the heat of the 

 operator's body near them would cause 

 a disturbance, and the adjustment is ef- 

 fected by rods and other ingenious mech- 

 anisms, which change the weights from 

 pan to pan or add the finer V-shaped 

 weights to the cross-beam to efl^ect a per- 

 fect balance. The operator stands at a 

 distance of lo feet (see page 153) and 

 reads the result through a telescope. 



One of the balances used in the volta- 

 meter work is so delicately adjusted and 

 sensitive to changes of temperature that 

 the operator cannot even remain in the 

 same room with it. It is kept in a room 

 guarded by double doors, in which a con- 

 stant temperature is preserved. The rods 

 by which it is controlled reach through 

 double glass panels into a second room, 

 which is also at an even temperature and 



guarded, too, by double doors. In fact, 

 to approach this balance is a ceremony. 

 One descends into the crypt ; four doors 

 have to.be unlocked in turn; lights have 

 to be lit ; and, finally, if one is specially 

 favored, the glass case which envelops it 

 may be opened for a brief inspection. 

 One feels that the poor thing suffers 

 physically when subjected to morbid cu- 

 riosity. 



Every precaution is taken that the 

 weights are not touched. They are kept 

 in glass cases and dusted with camel's- 

 hair brushes. Forceps are used to han- 

 dle the smaller weights, and lifters cov- 

 ered with chamois leather for the larger 

 ones, as the deposits from even the clean- 

 est hands would render them inaccurate. 



One division is conducting a series of 

 very important investigations upon the 



162 



