Mechanical Science, JffJ 



A great difference appeared when the sun's light was thrown 

 upon the north, or upon the south pole ; in the first case, power 

 was gained, and in the second lost, but the gain was, on an 

 average, greater than the loss. The heat communicated in these 

 experiments tended to diminish rather than increase power, and 

 cooling was found to be favourable. Tiie loss of power in a 

 south pole became less when it was removed out of the sun's 

 light J the gain of power in the north pole was increased by the 

 same circumstance. 



In the midst of these details, however, M. Zantedeschi states, 

 that he met with anomalies, and says, that magnets are a sort of 

 proteuses, which change under the eyes of the most careful 

 observer. 



A very singular fact, however, verified by numerous repe- 

 titions, was that on days when the sun was hid by thin clouds, 

 the south pole, subjected to its concentrated rays, increased in 

 power J whilst the north pole, by similar treatment, lost force. 

 This extraordinary eflfect is hypothetically accounted for, by 

 supposing that light has a negative polarity , which is inversely 

 as the layers of clouds floating in the atmosphere. 



Experiments were then instituted, like those of Mr. Christie, 

 in which it was found, that the direct light of the sun diminished 

 the arcs of oscillation of a vibratory magnetic needle. These 

 eflFects were obtained, and Mr. Christie's remarks confirmed. 

 M. Zantedeschi endeavoured to ascertain whether here also, the 

 exposition of the north or south pole to the light made any dif- 

 ference. A series of experiments, repeated above thirty times, 

 shewed that when the north pole was exposed, a greater number 

 of oscillations and a smaller amplitude were obtained, than when 

 the south pole was exposed. Still, it was remarked that, on those 

 days, when a thin veil of clouds covered the sun, the results were 

 inverted. — Bib. Univ. xlii. 193. 



8. Non-interference of different Electric Currents. — Professor 

 Marianini has been led to examine what might take place when 

 electric currents are so directed as to cross each other, with a 

 view of ascertaining whether there might be any interference ; 

 but he finds none, and in this respect, draws a strong analogy 

 between electricity and light ; the rays of the latter, as is well 

 known, crossing each other in almost all directions, as if quite 

 indifferent. 



At first, by attaching two zinc and two copper plates to the 

 sides of a cube of wood, and connecting them into cross pairs by 

 wires, and plunging them into a vessel of acid, it was found that 

 whether one or both pairs were connected, not the slightest dif- 

 ference resulted in the strength of the current in the wires when 

 examined by a magnetic needle : here, therefore, was no inter- 

 ference. 



