116 Mr King on a New Self-registering Thermometer. 



place the instrument in such an inclined position that the point 

 C will cease to be immersed among the mercury ; remove the 

 hand, and allow the thermometer to remain in that position for 

 a few minutes, till the mercury in A has descended as low as 

 the temperature of the air at the time ; hang it up, and it is 

 again arranged for another observation. This thermometer 

 may be made without the alcohol, and the space in the tube 

 which it occupies may be entirely filled with atmospheric air ; 

 but the indications would not then be so correct, on account 

 of the extreme elasticity of the inclosed air. A horizoutal posi- 

 tion may, however, correct that objection. At first sight the 

 fabrication of this instrument may appear difficult ; but if the 

 two legs are made and filled separately, then joined at F, its con- 

 struction and adjustment will, I conceive, be sufficiently simple. 



Another plan has also suggested itself to me, which I think 

 more simple, and may answer the purpose equally well, which 

 I will explain in a few words. The tube and bulb A, (Fig. 8,) 

 is a common thermometer, with a scale graduated in the 

 usual manner, and the top formed into a ball F, for the sake of 

 uniformity. (Fig. 9) is the bulb D, and part of the tube B 

 on a larger scale. The tube B and under ball are completely 

 filled up to the point C, which is open ; over which point is 

 fixed the bulb D, which is partially filled with fluid, say up to 

 the dotted line. For the scale of the tube B, number the de- 

 grees downwards from the point C, making it the zero of the 

 scale; ascertain the space between each degree, in the same 

 manner as is done in the case of a common thermometer ; hang 

 up this thermometer, and, should the temperature rise, a quan- 

 tity of the fluid will be pressed out of the tube at the point C, 

 and fall among the fluid in the bulb D. When the temperature 

 again falls, the number of degrees which the fluid is deficient 

 in the tube B, being added to the degrees of temperature 

 indicated by the attached thermometer A, will give the ex- 

 treme height of temperature the surrounding medium has 

 been at since the last arrangement of the instrument. The 

 manner of adjusting it is obvious, and its construction is so 

 exceedingly simple, that it must suggest itself to the glass- 

 blower, on the plan being distinctly explained to him. 



New South Wales, Sydney, August 1, 1827. 



