NATURAL PHILOSOPHY. 137 



will be of value in manufacturing chemistry. The principle is to 

 cause a current of heavy paraffin e oil to circulate, first through a 

 coil of pipes in a furnace, and then through the jackets of the 

 pans. It moves by its own convection. Any temperature from 

 100 to 700 Fahrenheit can easily be obtained. As contrasted 

 with steam heat, the inventor claims for his process a saving of 80 

 per cent, in fuel, the large amount of heat necessary to convert 

 water at 212 into steam being economized. 



DEEP-SEA THERMOMETERS. 



Capt. Richards, R.N., Hydrographer of the Admiralty, has 

 made a number of experiments regarding the inaccuracy of ther- 

 mometric measurements at great depths. As it is well known 

 that a delicate thermometer is affected in vacuo, it was naturally 

 supposed that an opposite effect would take place under in- 

 creased pressure. The experiments were performed with a hy- 

 draulic press. Previous to the experiments, Dr. W. A. Miller 

 proposed a mode of protecting the bulb from compression by en- 

 casing the full bulb in glass, the space between the case and bulb 

 being nearly filled with .alcohol. A wrought-iron bottle had been 

 made to contain a thermometer, for the purpose of comparison 

 with those subjected to compression, but it burst under the great 

 pressures employed. Those designed by Dr. Miller, however, 

 showed so little difference under pressure that they were received 

 as standards. Two series of experiments were then made at 

 pressures equal to depths of 250, 500, etc., to 2,500 fathoms, the 

 results of which satisfactorily proved that the strongest-made un- 

 protected thermometers are liable to considerable error, and 

 therefore that all previous observations made with such instru- 

 ments are incorrect. Experiments were also made in the testing 

 apparatus, with Sir William Thompson's enclosed thermometers, 

 to ascertain the calorific effect produced by the sudden compres- 

 sion of water, in order to find what error, if any, was due to 

 compression in the Miller pattern. An error was proved to exist, 

 but small, amounting to no more than 1.4 under a pressure of 

 3 tons to the square inch. The dredging cruise of the "Por- 

 cupine " afforded an opportunity of comparing the results of the 

 experiments made in the hydraulic testing apparatus with actual 

 observation in the ocean. The result was, that though there was 

 a difference in the curves drawn from the two modes of observa- 

 tion, still the general effect was the same, and the means of the 

 two were identical. From these experiments and observations a 

 scale has been made, by which observations made by thermome- 

 ters of similar construction to those with unprotected bulbs can 

 be corrected and utilized. It is suggested, that to avoid error 

 from the unsatisfactory working of the steel indices of self-regis- 

 tering thermometers, two instruments should be sent dow^i at 

 each observation ; and, although their occasional disagreement of 

 record may raise a doubt, a little experience will enable the ob- 

 server to detect the faulty indicator, while their agreement will 

 create confidence. 

 12* 



