80 Proceedings of the Royal Society 
condition of the instrument. It is obvious that any control which 
an observer may have over an instrument separated from him by, it 
may be, three or four miles of cord, is very limited, and is, in fact, 
confined to his ability to move it towards or from him. By a simple 
mechanical contrivance this longitudinal motion may be made to 
produce one of rotation, and, in fact, the assistance afforded by the 
observer to the thermometer to enable it to register its own tem- 
perature consists in his turning it either upside down or through a 
whole circle when it has reached the desired depth. The first 
observer who made use of this device was Aime. His working 
arrangement is described in Ann. Chim. Phys. 1843 [3] vii. p. 497. 
It is worked by a weight, which is allowed to slip down the line, 
and which then sets free the apparatus. His thermometre a bascule , 
along with a number of ingenious modifications of existing forms, is 
described in the same journal, 1845 [3] xv. p. 5. It was unfortu- 
nately only after he was obliged to leave the Mediterranean, w T hich 
had been the scene of his labours, that he invented the very elegant 
combination of thermometers by which he was enabled to ascertain 
the temperature at any depth, no matter what the- intervening dis- 
tribution might be. It is described in the memoir just cited. It 
consists of two outflow thermometers, so constructed that the one 
of them registers the sum of the rises of temperature, and the other 
the sum of the falls of temperature, to which it is exposed in any 
excursion. When they have reached the required depth they 
are inverted, and on their way back to the surface they register, 
as above described, the rises and falls of temperature to which they 
are exposed. If r be the sum of the rises of temperature, and 
/ the sum of the falls, s the temperature of the surface, then 
the temperature at the depth where they were inverted will be 
d = s + r - f. 
If they are allowed to register on the way down, and then in- 
verted at the greatest depth, so as not to register on the way up, 
the effect will be precisely the same, though the functions of the 
thermometers will be reversed. 
Beautiful and ingenious as Aime’s thermometers are, they have 
the disadvantages common to all outflow thermometers ; they are 
neither simple enough nor handy enough for work involving many 
observations. The inverting thermometer, patented by Messrs 
