1 62 THE SCIENTIFIC PAPERS OF 



drical copper vessel, on one side of which a mercury thermometer 

 is fixed in a suitable frame ; the bulb and lower part being 

 protected by a perforated shield. There are two funnels for 

 supplying hot and cold water respectively. The cold water pipe 

 ends near the top of the vessel, and is bent outwards, so that the 

 cold water entering and falling to the bottom may distribute itself 

 as it falls. The hot water pipe, on the other hand, ends at the 

 bottom of the vessel, so that the hot water may rise and diffuse 

 itself. In addition to this, the latter pipe- is provided with a 

 flexible tube, through which air is blown from the mouth, and 

 bubbling up through the water keeps it well mixed and of uniform 

 temperature.* 



"When the deflection of the galvanometer needle is towards the 

 left it indicates that the bath is too cold, and vice-versa. The 

 operator then adds hot or cold water, as the case may be, until the 

 balance of electrical resistance is established, when the mercury 

 thermometer gives a true reading of the temperature at the distant 

 place. 



By the use of a similar arrangement of apparatus and burying 

 the resistance thermometers at various depths in the ground, 

 the temperature may, without disturbing the coils, be registered 1 

 with the utmost accuracy at different periods from year's end to 

 year's end. In like manner, the temperature of the atmosphere at 

 elevated points may be registered in a consecutive manner. 



RESISTANCE COIL PROTECTED AGAINST WATER. In con- 

 structing a thermometer adapted for measuring deep-sea tem- 

 peratures it was necessary to fulfil the following conditions : 

 ( 1 ) The resistance must increase or decrease with a higher or lower 

 temperature, sufficiently to allow of an exact reading to one-tenth 

 of a degree Fahrenheit. (2) The wire must be so protected 

 mechanically that, under the pressure of a column of water of 

 3,000 fathoms, it would remain perfectly insulated. And (3) the 

 wire must be so coiled as to be readily affected by slight changes of 

 temperature in its vicinity. To effect this, a fine iron or copper 



* Since the above was written, I have adopted a modified arrangement of this 

 apparatus shown in Fig. 5, Plate 13. It consists of a plain cylindrical vessel, 

 into which a moveable tube is immersed, containing the coil and the mercury 

 thermometer. A flange at the bottom of the tube serves to agitate the water in 

 moving the tube up and down, and thus serves to equalize the temperature of the 

 liquid. 



