226 SEC. 8. HEAT. 



1051. Apparatus for determining the temperature effusion. 

 (Compare the adjoined description.) Prof. Dr. Himly, Kiel. 



1052. Air Thermometer on the plan of Jolly. Compare 

 PoggendorfPs Annalen, Jubelband, 1873. 



University of Munich (Prof. v. Jolly). 



lO52a. Original Air Thermometer, by Mr. Regnault. 



College of France. 



1053. Thermopile on the plan of Melloni of 64 bismuth anti- 

 mony elements. Wesselhoft, Halle. 



1054. Thermometer Stick for measuring temperatures at 

 some depth. Ludwig Meyer, Berlin. 



The instrument, adapted for depths down to 3 feet, is chiefly distinguished 

 by the strength of its construction. 



The bulb is in the nickel clamp, which latter stands by means of mercury 

 in thermal connexion with the bulb. This mercury serves also as buffer to 

 the thermometer bulb. 



The horn clamp is replaceable by an iron screw, which facilitates the intro- 

 duction of the thermometer into the ground. 



Care is taken that only the clamp be thermo-conducting, not the whole 

 tube. 



1055. Milligrade Thermometer. The milligrade scale is 

 one in which the interval of temperature between the freezing 

 and boiling points of mercury is divided into one thousand 

 degrees. 



According to Dulong and Petit, mercury freezes at 39-44 C., and boils 

 at + 360 C. For convenience, assuming that the freezing point is 40 C., 

 the interval is therefore 400 degrees C., thus it follows that 2^ degrees 

 milligrade are equal to 1 degree centigrade. Upon this scale the following 

 results are obtained. Water freezes at 100 M. and boils at 350 M., the 

 interval 250 being just one-fourth of the interval between the freezing and 

 boiling points of mercury. Many other substances also show a curious 

 relation in the interval between their freezing and boiling points to that of 

 mercury, facts which are not obvious upon other thermometric scales. 



The practical advantages of this system of graduation consist in the com- 

 parative smallness of the degrees, thus avoiding in many cases the necessity 

 of the use of fractions to express the boiling point of substances ; also that 

 the zero point being so low the scale is a continuous one, all numbers under 

 100 M. representing temperatures below freezing water, but avoiding the 

 necessity of the use of the minus sign, and at higher temperatures as 1,000 

 is approached, giving a clear idea that the heat is arriving at the extreme 

 limit of thermometric registration. 



In practically graduating this thermometer reference is not made to the 

 freezing or boiling points of mercury, but the freezing point of water is 

 marked as 100, and the boih'ng point as 350, and the scale carried upwards 

 or downwards as required. 



The conversion of centigrade degrees into milligrade degrees, or vice versS, 

 is extremely simple. A centigrade degree multiplied by 2, and 100 



