80 MR. T. HOPKINS ON IMPROVEMENT 
of this fall? Meteorologists point to the movements of 
the thermometer, and to the changes in tension of vapour, 
and endeavour to find in them an adequate cause for the 
reduction of atmospheric pressure which then occurs. 
But the registrations of their instruments have been of 
such a kind as to make this reference unsatisfactory, and 
have consequently permitted vague and insufficient expla- 
nations to be given by some, and to be received by others. 
These explanations have proceeded on the assumption 
that the fall of the barometer was to be accounted for by 
the alterations which take place in temperature and in 
vapour pressure, though this assumption may from many 
of these registers be shown to be erroneous. Of these, the 
observations made at Toronto in the year 1846, and pub- 
lished by the government, may be deemed the most suit- 
able for our present purpose. 
The whole Toronto observations extend over the years 
1846-7-8; but in order to have a case sufficiently simple 
to admit of being dealt with in the present paper, while it 
is a fair specimen of what occurs in many parts of the 
world, I will extract the hourly registrations of the baro- 
meter from four o’clock in the morning until ten at night 
of each day during the month of July in the year 1846, 
and then give in the same tabular form, for the same time, 
the recorded amount of tension of vapour, as deduced from 
the dew-point. The tension of vapour being then sub- 
tracted from the total atmospheric pressure as shown by 
the barometer, the remainder corresponds, according to 
the present views of meteorologists, to the separate pres- 
sure of the atmospheric gases, which is also given in 
another line. Having appended the corresponding tem- 
peratures as recorded from a standard thermometer, we 
may proceed to examine how far the results harmonise 
with the views of meteorologists. — (See the Table.) 
