312 M. Faraday o?i Cheltenham Water. 



The following are a few of Mr. Harvey's results : 



A pocket chronometer which possessed a steady rate of 

 + 1"*6, under the ordinary circumstances of the atmosphere, 

 had its rate increased to + 6"*2, when the density of the air 

 was diminished to a quantity represented by 20 inches of 

 quicksilver ; and on afterwards placing it in air of a density 

 denoted by 10 inches of mercury, a further increase of its rate 

 to + 1 1"'0 took place. On restoring the time-keeper to the 

 ordinary circumstances of the atmosphere, its rate returned 

 to +2"'l. 



In another set of experiments, with the same chronometei , 

 Mr. H. placed it in a condenser, under an atmospheric pres 

 sure of 45 inches, when its rate changed to — 4"*4 ; and 

 on increasing the density of the air to a quantity denoted by 

 60 inches of mercury, the daily variation further declined to 

 -8"-2. 



In another remarkable experiment, Mr. H. found that 

 when the rate of a chronometer was + 23"*5, under a receiver 

 having its air exhausted to a quantity denoted by half an inch 

 of mercury, the rate was altered to — 1 7"*2, when the air was 

 increased to a density corresponding to 75 inches of quick- 

 silver ; the rate of the time-keeper, under the ordinary cir- 

 cumstances of atmospheric pressure, being + 4"*7. 



Mr. H. has, we understand, drawn trom it several im- 

 portant conclusions; for instance, that a chronometer con- 

 structed in London, nearly on the level of the sea, would un- 

 dergo an alteration of rate, from difference of atmospheric 

 pressure alone, if transported to Geneva, to Madrid, to 

 Mexico, or any other place, situated much above the level of 

 the place where it was constructed. 



The whole of the results are about to be laid before the 

 Royal Society. 



NOTE ON THE EXISTENCE OF A NITRATE AND A SALT OF 

 POTASH IN CHELTENHAM WATER, BY M. FARADAY, &C. 



Having undertaken at the request of Dr. Creaser an ex- 

 amination of some water from Cheltenham, I had occason to 

 remark in it the existence of two substances not before ob- 

 served in waters from that place ; and though of no import- 

 ance in a medicinal point of view, yet as relates to the sources 

 from whence the waters obtain their impregnations, and to 

 the illustration they afford of the use of two tests suggested by 

 Dr.Wollaston, but not very frequently, I believe, in the hands 

 of chemists, they may I think possess interest ; one of these 

 substances is nitric acid, and the other potash. 



The source from which the water was obtained is called, I 



believe, 



