Curiosities of Science. 197 



oxidated magnets, it diminished in those which were not oxi- 

 dated, the diminution becoming insensible when the loadstone 

 was highly polished. He now concentrated the solar rays upon 

 the loadstone by means of a lens ; and he found that, both in 

 oxidated and polished magnets, they acquire strength when 

 their north pole is exposed to the sun's rays, and lose strength 

 when the south pole is exposed. /Sir David Bi 



COLOUR OF A BODY AND ITS MAGNETIC PROPERTIES. 



Solar rays bleach dead vegetable matter with rapidity, while 

 in living parts of plants their action is frequently to strengthen 

 the colour. Their power is perhaps best seen on the sides of 

 peaches, apples, &c., which, exposed to a midsummer's sun, 

 become highly coloured. In the open winter of 1850, Mr. Adie, 

 of Liverpool, found in a wallflower plant proof of a like effect : 

 in the dark months there was a slow succession of one or two 

 flowers, of uniform pale yellow hue ; in March streaks of a 

 darker colour appeared on the flowers, and continued to slowly 

 increase till in April they were variegated brown and yellow, 

 of rich strong colours. On the supposition that these changes 

 are referable to magnetic properties, may hereafter be explained 

 Mrs. Somerville's experiments on steel needles exposed to the 

 sun's rays under envelopes of silk of various colours ; the mag- 

 netisation of steel needles has failed in the coloured rays of the 

 spectrum, but Mr. Adie considers that under dyed silk the ef- 

 fect will hinge on the chemical change wrought in the silk and 

 its dye by the solar rays. 



THE ONION AND MAGNETISM. 



A popular notion has long been current, more especially on 

 the shores -of the Mediterranean, that if a magnetic rod be 

 rubbed with an onion, or brought in contact with the emana- 

 tions of the plant, the directive force will be diminished, while 

 a compass thus treated will mislead the steersman. It is diffi- 

 cult to conceive what could have given rise to so singular a 

 popular error.* Humboldt's Cosmos, vol. v. 



DECLINATION OF THE NEEDLE THE EARTH A MAGNET. 



The Inclination or Dip of the Needle was first recorded by 

 Robert Norman, in a scarce book published in 1576 entitled The 

 New Attractive; containing a short Discourse of the Magnet or 

 Loadstone, &c. 



Columbus has not only the merit of being the first to dis- 

 cover a line without magnetic variation, but also of having first 



* This is mentioned in Prodi Diadochi Paraphrasis Ptolem., 1635. (Delambre, 

 Hist, de I' Astronomie ancienne.) 



