318 PHILOSOPHICAL TRANSACTIONS. j^ANNO I698. 



first tried it after the usual manner, with galls, and found it turned almost 

 quite black, though it had been brought at least 30 miles by land-carriage from 

 Eglingham in Northumberland. But I was much more surprised to find, after 

 I had slowly in a glass evaporated more than one half of this water, that it 

 still retained the same black quality, and struck yet as deep with galls as ever. 

 The strangeness of this phenomenon made me hope to meet with somewhat 

 new and uncommon in this water, and the event did not deceive me, for it 

 yielded me at least a real and genuine vitriol. I say nothing of the ochre which 

 this water let fall in very great plenty, that being a thing common to all atra- 

 fnentous waters. 



Though greatly surprised at this phenomenon, I could not bring myself to 

 think it possible that the pyrites lying constantly under water, should ever yield 

 vitriol, and I knew of nothing else (at least in England) that I could expect it 

 from. But having to visit this remarkable well, I found our vitriol water to 

 be only an old drift made for the draining of a row of old wrought coal-pits a 

 little above, and I informed myself from some old men, that had formerly 

 wrought in these pits, that there was plenty of the pyrites there, by them 

 called brass lumps: and that this drift was sometimes dry, and sometimes run 

 with a plentiful stream ; which is as fair and full an account how this water 

 comes to have vitriol in it, as any one need to desire. Dr. Cay found soon 

 after another similar instance, of a reputed fons vitriolaceus, near Haigh in 

 Lancashire, which turned out to be nothing more than a like drift to drain the 

 water from the coal works there. 



On the Longitude of Canton. By M. Cassini, N° 245, p. 371- 



From the transit of Mercury over the sun's disk, observed at Canton and 

 Nuremberg ; and again from the eclipses of the moon, observed at Nuremberg 

 and Paris, M. Cassini has determined the difference of longitudes between Can- 

 ton and Paris to be 7h. 23m. or 110° 45'. 



The Quadrature of the Logarithmic Curve. Bij Mr. John Craig. N° 245, 

 p. 373. Translated fro7n the Latin. 



Let ONF (fig. 7, ph 5) be a logarithmic curve, whose asymptote is ar, in 

 which let a point a be taken, such, that its first ordinate ao may be equal to 

 the subtangent, or to unity : to determine the curvilineal space aonm, compre- 

 hended by the two ordinates ao, mn, the absciss am, and the logarithmic curve 

 on. From o draw oe parallel to am and cutting mn in e ; then the rectangle 

 of the segments me, en, will be equal to the required space. 



