. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. ted, andthe repulsion will be plainly distinguished. It is unnecessaryin dia-magnetic projections, that more than the magneticpole terminals should be seen in the field. The various heaping of liquids, according to their mag-netic character, is fairly visible in profile; but by turning themagnet so as to lie horizontally on the vertical attachment,the heaping of liquids in a thin watch-glass will be con-spicuously shown by the strong refraction produced at theinclined surfaces. 237. Static C
. Optical projection : a treatise on the use of the lantern in exhibition and scientific demonstration. ted, andthe repulsion will be plainly distinguished. It is unnecessaryin dia-magnetic projections, that more than the magneticpole terminals should be seen in the field. The various heaping of liquids, according to their mag-netic character, is fairly visible in profile; but by turning themagnet so as to lie horizontally on the vertical attachment,the heaping of liquids in a thin watch-glass will be con-spicuously shown by the strong refraction produced at theinclined surfaces. 237. Static Charges.—Most simple phenomena of thischaracter are demonstrated by projecting an electroscope,especially of the gold-leaf kind, as shown in fig. 81. Staticinduction is readily shown in the same way. All the usualexperiments with suspended pith-balls, chimes, feathers, hair,&c, are too obvious to need any explanation. Any apparatuswhich cannot be reduced to the size of the condensers, or thelens in fig. 106, may generally be projected by the shadowmethod (§ 109). MAGNETISM AND ELECTRICITY 397. Quantitative measurement is more difficult, but has lately used a pendulum electroscope in a form thatmakes a most sensitive electro-meter. He suspends a giltpith-ball I cm. radius (built upof small pieces cemented) adistance of 364 cm. from theceiling, by two silk fibresfastened 52 cm. apart andmeeting at the ball, behindwhich a scale is arranged. Abrass ball of the same size ismounted on a glass rod, var-nished while warm withparaffin wax. A force of onlyone dyne acting on the sus-pended ball deflects it 133mm.; and charging both ballsin contact so as to give thesame charge to each, thecharge c on either was foundin absolute electrostatic unitsby the formula IT 1-8 where d is the distance incm. between the centres ofthe balls, and d the deflectionfrom the vertical in d is over 5j cm. thelaw of inverse squares wasdemonstrated within 1 percent; and by using a proof-pl
Size: 1309px × 1909px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorwrightle, bookcentury1900, bookdecade1900, bookyear1906
