Mr. Horsburgh’s Observations on a 
barometers, one made by Troughton, the other by Ramsden, 
and a thermometer by Frazer. These were placed exposed 
to a free current of air in a cabin, where the basons of the 
barometers were 13 feet above the level of the sea. 
The hours at which the heights of the barometers, and ther- 
mometers were taken, viz. noon, iv hours, x hours, xn hours, 
xvi hours, and xix hours, were chosen, because at these times 
the mercury in the barometer had been perceived to be regu- 
larly stationary between the tropics, by former observations 
made in India in 1800 and 1801. It was found that in settled 
weather in the Indian seas, from 8 AM to noon, the mercury 
in the barometer was generally stationary, and at the point of 
greatest elevation ; after noon it began to fall, and continued 
falling till 4 afternoon, at which time it arrived at the lowest 
point of depression. From iv or v PM the mercury rose again, 
and continued rising till about ix or x PM, at which time it 
had again acquired its greatest point of elevation, and con- 
tinued stationary nearly till midnight ; after which it began to 
fall, till at iv AM it was again as low as it had been at iv after- 
noon preceding ; but from this time it rose till 7 or 8 o'clock, 
when it reached the highest point of elevation, and continued 
stationary till noon. 
Thus was the mercury observed to be subject to a regular 
elevation and depression twice in every 24 hours in settled 
weather ; and the lowest station was observed to be at about 4 
o’clock in the morning and evening. I remarked that the 
mercury never remained long fixed at this low station, but 
had a regular tendency to rise from thence till towards 8 
in the morning and about 9 in the evening, and from those 
times continued stationary till noon and midnight. 
