1874.] on a New Deep-sea Thermometer. 239 



by minimum thermometers sunk to the bottom of the sea, even if their 

 registration were unaffected by the pressure, would only give the lowest 

 temperature reached somewhere between top and bottom, not necessarily 

 at the bottom itself. The temperatures at various depths might indeed 

 (provided they nowhere increased on going deeper) be determined by a 

 series of minimum thermometers placed at different distances along the 

 line, though this would involve considerable difficulties. Still, the 

 liability of the index to slip, and the probability that the indication of 

 the thermometers would be affected by the great pressure to which they 

 were exposed, rendered it very desirable to control their indications by 

 an independent method." Again, at page 299, we find : " I ought to 

 mention that in taking the bottom temperature with the Six's thermo- 

 meter the instrument simply indicates the lowest temperature to which 

 it has been subjected ; so that if the bottom water were warmer than 

 any other stratum through which the thermometer had passed, the 

 observations would be erroneous." Undoubtedly this would be the case 

 in extreme latitudes, or in any spot where the temperature of the air is 

 colder than that of the ocean. Certainly the instrument might be 

 warmed previous to lowering ; but if the coldest water should be on the 

 surface, no reading, to be depended upon, could be obtained. 



It was on reading these passages in the book above referred to that it 

 became a matter of serious consideration with us whether a thermometer 

 could be constructed which could not possibly be put out of order in 

 travelling or by incautious handling, and which should be above suspicion 

 and perfectly trustworthy in its indications. This was no very easy task. 

 But the instrument now submitted to the Eellows of the E-oyal Society 

 seems to us to fulfil the above onerous conditions, being constructed on 

 a plan different from that of any other self-registering thermometers, 

 and containing as it does nothing but mercury, neither alcohol, air, nor 

 indices. Its construction is most novel, and may be said to overthrow 

 our previous ideas of handling delicate instruments, inasmuch as its 

 indications are only given by upsetting the instrument. Having said 

 this much, it will not be very difficult to guess the action of the thermo- 

 meter ; for it is by Upsetting or throwing out the mercury from the in- 

 dicating column into a reservoir at a particular moment and in a par- 

 ticular spot that we obtain a correct reading of the temperature at that 

 moment and in that spot. First of all it must be observed that this in- 

 strument has a protected bulb, in order to resist pressure. This pro- 

 tected bulb is on the principle devised by us some sixteen years since, 

 when we supplied a considerable number of thermometers thus protected 

 to the Meteorological Department of the Board of Trade ; and they are 

 described by the late Admiral EitzEoy in the first Number of the 

 ' Meteorological Papers,' page 55, published July 5th, 1857. Eeferring 

 to the erroneous readings of all thermometers, consequent on their 

 delicate bulbs being compressed by the great pressure of the ocean, he 



