Mr. T. Hopkins on the Meteorology of Bombay. 471 



ture increases greatly, as much as nearly seven times the 

 amount that it previously fell, whilst the dew-point, although 

 it also rises, does not rise to quite double the extent that it 

 fell in the two hours ; yet notwithstanding these great altera- 

 tions, amounting to complete reversals of the two influences 

 that are in operation, the barometer continues to rise, and 

 attains an increase of "047. These facts, however, taken 

 together, show that temperature, as measured by the thermo- 

 meter near the surface of the earth, produces little comparative 

 effect on the amount of atmospheric pressure; and that the 

 alteration of vapour pressure must have had much greater in- 

 fluence than alteration of temperature as measured by the 

 thermometer, and must have produced the rise of the baro- 

 meter from six to ten o'clock. 



Proceeding to the next six-hour stage of the daily fluctua- 

 tions of the barometer, we find that from ten to two o'clock, 

 the first four of these six hours, temperature advances 2°*3, 

 and reaches its highest point for the day at the last-named 

 hour ; and the dew-point, indicating vapour pressure, also 

 rises as much as '024. Here it appears that vapour pressure 

 increases so much as *024, whilst temperature advances only 

 2°*3; alteration of vapour pressure therefore should, in ac- 

 cordance with what had occurred previously, be now more 

 powerful than alteration of temperature, and should further 

 increase the whole atmospheric pressure, and cause the baro- 

 meter to rise higher than the point it had previously reached, 

 as the theory we are examining teaches it ought to do; but 

 instead of rising the barometer falls no less than *076; so that 

 from six to ten o'clock, whilst 



a rise of temperature of 3 0, 4 ("jointly produced al 

 and a rise of the dew- < rise of the baro- > "047 



point of . . . . •021^ meter of J 



in the following four hours, from ten to two o'clock, 

 a rise of temperature of . -2 0, 3 /"produced a fall of 1^„ 

 and a rise of the dew-point of *024 \_ the barometer of J 

 Thus, where the vapour pressure is relatively weak, we see 

 that the barometer rises; and where it is relatively strong the 

 barometer sinks, — being the reverse of that which must have 

 taken place if the temperature theory were correct. 



Again, from two to four o'clock p.m. the temperature sank 

 •2 and the dew-point rose "005. Thus during these two hours 

 the alterations which took place in both the temperature and 

 the dew-point were such as from the operation of each of 

 their influences ought, on the temperature theory, to have 

 caused the barometer to rise. But it did not rise; on the 

 contrary it fell, — no less than *021. These facts prove most 



