88 THE VOYAGE OF H.M.S. CHALLENGER. 



limited. By a simple mechanical contrivance vertical motion may be made to produce 

 one of rotation, and, in fact, the assistance thus afforded by the observer to the ther- 

 mometer to enable it to register its own temperature 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 such a device was Aime\ By allowing a weight to slip 

 down the line the upper attachment of his thermometer was set free and it fell over. The 

 change thus produced was the means of registering the temperature at the depth. 1 His 

 thermometre d bascule, along with a number of ingenious modifications of existing forms, 

 is described in the same journal. 2 It was unfortunately only after he was obliged to 

 leave the Mediterranean, which 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 distribution might be. It is 

 described in the memoir just cited. It consists of two outflow thermometers, so con- 

 structed that 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, f the sum of the falls, 

 and 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 inverted 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 Aimers thermometers are, they have the disadvantages 

 common to all outflow thermometers ; they are neither simple enough nor handy enough 

 for work involving many observations. 



During the course of the voyage Messrs. Negretti & Zambra patented an instrument 

 which promised to fulfil the conditions required of a thermometer for isolated observations. 

 Staff-Commander Tizard made an extensive series of experiments with it under various 

 conditions, of which he gives the following account : — 



" Messrs. Negretti & Zambra's instrument for ascertaining temperatures is a 

 mercurial thermometer (see fig. 29 C), the tube of which is contracted at the point D, 

 so that when the instrument is held upside down the mercurial column separates at 

 that point and falls to the bottom in the enlarged part of the tube E. If a complete 

 revolution of the thermometer be slowly made, the portion of mercury separated falls 

 over into the tube F, which is graduated so as to register the exact amount 

 separated when the instrument is reversed. By attaching this thermometer to 

 machinery which reverses it at a certain time, or at a certain depth, the temperature 

 at that time or depth is registered. To readjust the instrument all that is required 



1 Ann. d. Chim., b&t. 3, t. vii. p. 497, 1843. 2 Ibid., t. xv. p. 5, 1845. 



