18 PHILOSOPHICAL TRANSACTIONS. [anNO 1683-4. 



weighed ]20lb. some of them 30lb. some 40lb. very hard, and of the colour 

 of iron.* 



Now this ferrum or aes nubigenum, if there was ever any such, was concreted 

 of the breath of the pyrites, which we have elsewhere shown to be the pyrites 

 ex tota substantia. The other instance, which I say is recorded in our registers, 

 is of lightning being magnetic : (See Philos. Trans. N° 127.) This I am sure 

 of, I have a petrified piece of ash, which is magnetic; that is, the pyrites in 

 succo; which makes it probable it may be magnetic also in vapour. 



The Effect of Thunder on the Compass of a Ship. Communicated by Sir R. S, 



N° 157, p. 520. 



July 24, ]681, the ship called the Albemarle, being 100 leagues from Cape 

 Cod, in latitude 48°, about 3 o'clock afternoon, met with a thunder storm. 

 The lightning burned the main-topsail, split the main cap in pieces, rent the 

 mast quite throughout; and there was in particular one dreadful clap of thunder, 

 with which something from the clouds fell on the stern of the boat, which broke 

 in many small parts, and split one of the pumps, the other pump being also 

 much hurt. It was a bituminous matter, smelling much like fired gun-powder: 

 it continued burning in the stern of the boat ; and it could not be extinguished 

 till all the matter was consumed. 



When night came, observing by the stars, they perceived that their com 

 passes were changed ; the north point of the compass in the binacle was turned 

 clear south. There were two other compasses unhung in the locker in the 

 cabin, in one of which the north point stood south, like that in the binacle ; in 

 the other, the north point stood west; so that they sailed 1000 leagues by a 

 needle, whose polarity was quite changed. As for the compass wherein the 

 lightning had made the needle to point westward, since it was brought to New 

 England, the glass being broken, it has, by means of the air coming to it, 

 wholly lost its virtue. 



y/rt Abstract of a Treatise on the Calculus Humanus ; in Answer to several 

 (Queries proposed by Sir John Hoskins. By Fred. Slare, M. D. F. R. S, 

 N° 157, p. 523. 



After combating the various opinions of other authors concerning the com- 

 position of the human calculus. Dr. Slare concludes — This concrete seems 

 rather referable to bone than to any other consistent or fluid part of the body, 



• On this subject, the falling of stones from the clouds, several interesting papers have appeared 

 in some of the late volumes of the Philosophical Transactions. 



