48& PHILOSOPHICAL TRANSACTIONS. [aNN0 1681. 



It is generally observed, that wherever mines of lead-ore are, there caverns 

 of various kinds and situations are found. The most considerable in Mendip- 

 hills is a cavern in a hill called Lamb. First a perpendicular shaft descends 

 about 10 fathoms, then you come into a leading vault, which extends itself in 

 length about 40 fathoms ; it runs not on a level, but descending, so that when 

 you come to the end of it you are 23 fathoms deep by a perpendicular line ; 

 the floor of it is full of loose rocks : its roof is firmly vaulted with lime-stone 

 rocks, having flowers of all colours hanging from them, which present a most 

 beautiful object to the eye, being always kept moist by the distilling waters. In 

 some parts the roof is about 5 fathoms in height, in others so low that a man 

 has much ado to pass by creeping; the width is mostly about 3 fathoms. This 

 cavern crosses many veins of ore. About its middle, on the east side, lies a 

 narrow passage into another cavern, which runs between 40 and 50 fathoms in 

 length. At the end of the first cavern there opens another large one. 



I have been in many other caverns upon Mendip-hills. The frequency of 

 caverns on those hills may be easily guessed at, by the frequency of swallow- 

 pits, which occur there in all parts, and are made by the falling in of the roofs 

 of caverns ; some of these pits being of a large extent, and very deep ; and 

 sometimes our miners, sinking in the bottom of these swallows^ have found 

 oaks 15 fathoms deep in the earth. 



On the F^ariation of the Needle ; and of the Phosphorus of Dr. Kunkel. By 

 J. Chr. Sturmius, Philos. Collect. N" 2, p. 8. 



After many trials repeated several days one after another, and with various 

 ways of examination, still in every one of them with the same success, he cer- 

 tainly found that the north end of the magnetic needle, which the former age 

 always reported to us to vary from the north, and to direct or point more to- 

 wards the east by several degrees, did now decline towards the west near 5 de- 

 grees. On the renewing of the Society of the Curiosi in Germany the third 

 time, I had occasion the last summer to make many experiments with the 

 pneumatic engine: among the rest, having prepared a large receiver of copper 

 of 2 feet diameter, made by joining two hemispheres together, so as that they 

 could at pleasure be separated again ; I made one trial not unpleasant : I sealed 

 lip a round glass hermetically, and covered it with a double bladder very care- 

 fully, and including it in the spherical receiver, I found that after about 200 

 exhaustions had been made, it broke all in pieces in the receiver with a very 

 great noise, by the elasticity of the air inclosed in the glass globe. 



