48 



NA TURE 



[Afaj' 1 6, 1872 



may take place when I complete the battery connection. 

 Thercsistance of both branchcircuitsbeing the same,no de- 

 llcclioncf Uie needle is observable on depressing the key, 



but when I pass the flame of a spirit-lamp under the one 

 platinum coil, the needle is thrown immediately over to 

 the risrht, because the electrical resistance of the heated 



needle. When I withdraw the spirit flame from the wire 

 the needle rapidly returns to its zero position, but in pass- 

 ing it under the other spiral wire the needle immediately 

 dcllects''in the opposite direction. 



If instead of using the open spirals I were to wind thin 

 insulated wire of any pure metal upon two small cylindri- 

 cal pieces of wood, and were to encloEc the tiny spirals in 

 small silver casings, as shown in view and in section by 

 Fig. 2, taking care that the extremities of the spiral wires 

 were soldered to thicker insulated wires leading respec- 

 tively to the battery and difterential galvanometer before 

 mentioned, it follows that no dellection of the needle 

 ensues when both the protected and equal spirals are 

 dropped into a jar containing iced water. But if I take 

 one of the spirals from the water, and place it, for in- 

 stance, by his kind permission, into the hands of our 

 President, without disconnecting the same from its lead- 

 ing wires, the balance of resistance will no longer take 

 place, and a deflection of the needle to the right actually 

 takes place. I will now endeavour, however, to re-estab- 

 lish the eciuilibrium by adding warm water to the iced 

 water surrounding the comparison coil near me until no 



wire is increased, and C( nsequcntly a larger piopcrtion of 

 the currtnt is passing through the cooler circuit, exer- 

 cising a preponderating influence upon the galvanic 



deflection of the needle is observable. This result being 

 obtained, it follows that the temperature of the water 

 surrounding the one coil must he identical with the tem- 

 perature of our President's hand, and the delicate mercury 

 thermometer which I have placed in my solution must 

 give me the temperature of the distant place which I in- 

 tended to measure. The temperature here observed is 

 89'5° Fahrenheit, which is at this moment that of Sir 

 Henry Holland's hands. This result is independent of the 

 ratio in vhich the electrical resistance increases with 

 temperature in the similar coils, and considering that the 

 silver casings containing the coils are not larger than small 

 pencil-cases, this method might be advantageously em- 

 ployed in physiological research. The one coil would only 

 have to be placed within the cavity to be measured, to 

 enable the observer to read the temperature from time to 

 time, without disturbing the patient, with the accuracy of 

 which the mercury or spirit of wine thermometer employed 

 is capable. But the same method is applicable for 

 measuring the temperatures of distant or inaccessible 

 places, such as the interior of stores or cargoes of materials 

 liable to spontaneous combustion, of points elevated above 

 the surface of the ground, or of great depths below for 



