VOL. LVII.] PHILOSOPHICAL TRANSACTIONS. 401 



will be dissolved ; the earth of which will be precipitated by the fixed alkali, and 

 by that means make the quantity of unneutralized earth appear greater than it 

 really is. 



It appears from these experiments, that the unneutralized earth is entirely 

 precipitated from these 3 waters, by the addition of a proper quantity of lime- 

 water ; as the trifling quantity found to be deposited, on the evaporation of 2 of 

 them, most likely proceeded only from not exposing the water to the air long 

 enough for all the lime to be precipitated. So that he thinks it seems reasonable 

 to conclude, that the unneutralized earth, in all waters, is suspended merely by 

 being united to more than its natural proportion of fixed air. 



To return to Rathbone-place water; it appears from the foregoing experiments, 

 that 1 pint of it, or 7315 grs. contains, 1st, as much volatile alkali, as is equiva- 

 lent to -jSj- grains of volatile sal ammoniac: 2dly, 8-rV grs. of unneutralized 

 earth, a very small part of which is magnesia, the rest a calcarious earth : 3dly, 

 as much fixed air, including that in the unneutralized earth, as is contained in 

 IQ-To- grs. of calcarious earth: 4thly, 1-^ of selenite: 5thly, 7-ro of ^ mixture 

 of sea salt and Epsom salt; and the whole solid contents of 1 pint of the water 

 isl7igrs. 



One pint of water, from the pump in Marlborough-street, contains 1-^ grs. 

 of unneutralized earth, and as much fixed air as is contained in 2-^ grs. of 

 calcarious earth. 



The same quantity of water, from the pump in Hanover-square, contains 2-J^ 

 grs. of unneutralized earth, with as much fixed air as is contained in 7-^ of 

 earth. 



The same quantity of water, from St. Martin's church-yard, contains 3-^ grs. 

 of unneutralized earth, with as much fixed air is contained in 8^ of earth. 



XJI. Of a Meteor seen at Oxford, Oct. 12, 17 66. By the Rev. John Swinlon, 



B. D., F. R. S. p. 108. 

 The Rev. Dr. Sharp coming into Christ-church common-room out of the 

 great quadrangle, Oct. 12, 1766, about S*' SO"* p. m. informed the company 

 there, that he had seen some remarkable Aurorae Boreales a few minutes before. 

 But, as such phenomena are common enough here, they gave little attention to 

 the information. Being on the terrace, about 8'' 46'" p. m. Mr. S. discovered a 

 broad luminous arch, in the northern part of the hemisphere, extending from e. 

 to w. almost terminated by the horizon, and somewhat less than a semicircle. 

 The upper or exterior limb of this arch, with a certain portion of the lucid 

 adjoining tract, was white and resplendent; but the brightness gradually decreased 

 as it approached the lower or interior limb, which was fuscous and obscure, that 

 it seemed scarcely distinguishable from the clouds that were contiguous to it. 



\OL. XII. 3 F 



