339 



This, which is one of the worst sets, must be imputed, like 

 the last, to those unaccountable uncertainties which affect ba- 

 rometric measurements, particularly in cases like this, where the 

 height is small, and one of the stations in a ravine liable to acci- 

 dental changes of temperature and partial currents of air. But 

 the inconsistency of the indications between spaces of five mi- 

 nutes is the point we have to remark, and the general charac- 

 ter of the series amply confirms the assumption with which we 

 set out. Theyall of the thermometer is continuous until the 

 last observation, when it rises 0°.l, and we notice an equally 

 regular rise in the column of differences till the last three ob- 

 servations, when it is very clear the atmosphere had been in- 

 fluenced by some agencies contrary to the decline of the diur- 

 nal temperature, which, though not indicated by the mass of 

 mercury till Obs. 28, had begun at Obs. 26 to influence the 

 magazine of hydrogen. Such a series as the one before us 

 shows how perplexing an instrument the sympiesometer must 

 sometimes be, since in this case, even after the tedious delay 

 of an hour, we should have the greatest difficulty in selecting 

 the height most to be depended on. 



The following I consider a very important series. 



Table III.— /w/^r 19j5^ (?) 1825. 



