•0» the Production of Vapor, 75 



^ences, there is mentiorjed a ver}' curious ol3scrvatioii on 

 the ascent and situation of tlie vapor, which arose at that 

 time, made by a gentleman at PcpperelL " About nine 

 o'clock (says he) in the morning, alter a sliower, the va- 

 pors arose from the springs in the low lands in great 

 abundance. I took notice of one large column, that as- 

 cended with great rapidit}^ to a considerable height above 

 the highest hills, and soon spread into a large cloud ; then 

 moved off a little to the Westward, A second cloud was 

 formed in the same manner from the same springs, but 

 .did not ascend so high as the first : and a third was form- 

 ed in the same places in less than a quarter of an hour 

 after the second." One of the gentlemen who observed 

 here, mentions a circumstance of somewhat a singular 

 nature. — " Whilst the darkness continued, (says he) the 

 clouds were in quick motion, interrupted, skirted one 

 over another ; so as apparently, and I suppose really, to 

 form a considerable number o^ strata.'''' As to the state 

 of the atmosphere. Professor Williams, who gave the ac- 

 count, observes, "that its gravity was gradually decreas- 

 ing the bigger part of the day." At Bradford, about 

 thirty miles North of Cambridge, and nearly under the 

 same meridian, the mercury in the Barometer stood at 6 

 o'clock, A. M. at 29 inches 82; at lOh. 20m. it was at 

 .29 inches 68 ; and at lOli. 45m. it stood at 29 inches 67 ; 

 at 12h. 15m. the mercury had fallen to 29 inches 65. — 

 Farenheit's thermometer at Bradford, at 6 o'clock, A. M. 

 was at 39^. At 12 oclocjk it stood at 51°. At Cam- 

 bridge, at 12 o'clock, it was 51^^ 1-2. 



These phenomena are the more noticeiible, because 

 they seem to take place contrary to the received law in 

 hydrostatics, that the tendency of a body to ascend or de^ 

 scend^ in a flu'id, is proportional to the difference between 

 the specific grav'ity of the body, cmd that of the fiuid. — 

 Therefore the denser a fluid is, the greater will be the fa- 

 cility with which a given body v/ill ascend in it. W^e 

 ■should be led to conclude from this, that the evaporation 

 ■would be the most abundant, when the gravity of the at- 

 mosphere is the greatest. But the reverse of this hap- 

 ^pens. What cause can be assigned that can produce 

 so unexpected an effect ? If it should be said that when 



