acceleration of the pendulum in different latitudes . 181 
of degrees above zero : the mercury in the thermometers, on 
the other hand, took up the temperature of the room within 
half an hour after their exposure. The clocks were put in 
motion on the 30th of April, and the account taken up on the 
4th of May, the room having been kept at about the tempe- 
rature of +45 0 for the preceding three days and nights. 
It proved however an erroneous supposition, that a sufficient 
interval to complete the observations would occur between the 
first return of mild weather, and the thorough breaking up 
of the frost : it was not indeed until the third week in May, 
that the weather became sufficiently settled or warm, to com- 
mence them to any purpose : during the first fortnight strong 
northerly winds prevailed with heavy snow drifts, preventing 
the reference to a meridian mark, and occasionally burying 
the house altogether beneath the drift snow ; when the only 
access to it was by digging down to the window of the room 
in which the clocks were going. It was desirable to keep the 
temperature of the room at about the same degree as in the 
experiments in London, namely, about 45 0 ; but the mean 
height of the thermometer in the air during this fortnight was 
not more than The walls of the house had been hung 
round with a double folding of canvass, and were well banked 
up with snow on the outside ; nevertheless, it was necessary to 
introduce the stove into the same room with the clocks to effect 
so great a difference of temperature, and even to place it not 
far distant from them. It will readily be imagined that a forced 
temperature of such amount, and under such circumstances, 
must have been liable to incessant fluctuation and uncertainty, 
as indeed it was. The thermometers were suspended in the 
clock cases in such manner that their bulbs were on a level 
