29 
of Edinburgh, Session 1872 - 73 . 
remained exactly at 55°, while the index in the maximum side 
stood in close contact with the mercury at 66°. This instrument 
is subject to an alternative inconvenience, requiring nice adjust- 
ment of the force of the spring attached to the indices. If they 
are too tight, they may stick beyond the force of the magnet to 
move them, or so that the mercury may pass instead of pushing 
them. If they are too loose, a slight shock may alter their posi- 
tion. To avoid this risk, the simplest precaution is to paint the 
last eighteen feet of the line white. As the rest becomes deep 
brown in the water, the winder-up of the reel is at once apprised 
of the necessity of gradually slowing his speed before the instru- 
ment appears near the surface. The time necessary for the 
thermometer to assume a new temperature is considerable, and 
ought to be ascertained experimentally. Mine, instead of twelve 
hours, like that of De Saussure, takes seven minutes to move six 
degrees in a gentle current of uniform temperature. It had 
seldom to pass through so many degrees between one observation 
and another ; but I allowed it always eight, and generally ten 
minutes, and in important observations near the bottom even 
fifteen or twenty minutes, for absolute security. But I believe 
ten minutes to be in all circumstances more than sufficient. 
The late Mr James Jardine, civil engineer, and during his 
lifetime a prominent Fellow of this Society, made in 1812 and 
1814 observations in Loch Lomond, Loch Katrine, and Loch 
Tay similar to De Saussure’s and my own. These valuable 
observations have been recovered by Mr Leslie, in the form of the 
original draught, and have been communicated to the Society 
by Mr Buchan; but I find that most of them had appeared in Sir 
John Leslie’s article Climate , in the “ Encyclopaedia Britannica,” 
and again in an octavo collection of Sir John’s treatises in that 
work, edited in 1838 by the late Principal Forbes. Jardine’s 
observations may yet turn out more valuable than he could have 
anticipated, and already seem to me of such interest as to deserve 
further notice. 
His experiments were made early in September. In Loch 
Lomond, in 1812 he found near the surface a temperature of 59°*3 ; 
at 240 feet, 41 0, 3; at the bottom, in 600 feet soundings, 41 T°. On 
Loch Katrine, the day previous, he found 57 0, 3 near the surface; 
