i46 PHILOSOPHICAL TRANSACTIONS, [aNNO 1738. 



the effluvia increased to such a degree, as to appear in mornings over the top 

 of the well, in the form of a mist, and gave great annoyance to those who 

 came within its sphere of action. From hence it is worth observing, that the 

 same damp, according to the variation of the weather, is specifically heavier or 

 lighter than the air. 



Concerning Magnets having more Poles than two. By Mr. John Eames, 



F. R. S. N" 450, p. 383. 



The sagacious Dr. Halley, in his account of the changes of the variation of 

 the magnetic needle, on the hypothesis of the earth's being one great magnet 

 having four magnetic poles, tells us, that he had found two difficulties not easy 

 to surmount; the one was, that no magnet he had ever seen or heard of, had 

 more than 2 opposite poles, whereas the earth had visibly 4, if not more, &c. 

 On looking over the copy of the Journal-book of this honourable society. 

 Vol. 2, an article is in the following words : 



July 20, 1664, " Mr. Ball produced several loadstones, and among them 

 two terrellas, whereof one seemed to have 4 poles, with a circle passing be- 

 tween them, of no virtue at all. Some of the company suggested, that it 

 was probable this stone consisted of two stones, by nature cemented together 

 by a piece that had no magnetical quality in it; and if single, whether the re- 

 spective poles were opposite." 



^n Account of some Magnetical Experiments, By J. T. Desaguliers. 



N° 450, p. 384. 



In the year 1715, trying some experiments on a very large weak loadstone, 

 the Dr. found that it had several poles. He then tried several other loadstones, 

 and often found 4 poles in such as had been armed when he took off their 

 armour. In large coarse stones he found sometimes 8, 9, or 10 poles. This 

 made him believe that all loadstones had several poles; but when he tried Lord 

 Paisley's loadstones, and other very good ones, he then found that homogene- 

 ous loadstones had but 1 poles ; those that have more being only an aggregate 

 of magnetic and other matter, which makes a heterogeneous substance. Such 

 is the society's great loadstone; for it has several poles. 



An Account of some Magnetical Experiments made before the Royal Society, 

 By the Rev. J. T. Desaguliers, LL. D. F. R. S. N° 450, p. 385. 



Dr. D. took a bar of iron, of l-4th of an inch diameter, which having been 



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