February 3, 1905.] 



SCIENCE. 



167 



availed themselves of the results of the 

 magnificent work that has been done in 

 this field in Europe, more especially at the 

 Bureau Internationale and the Reichsan- 

 stalt, and by the thermometer makers of 

 France and Germany. For our present 

 purpose thermometers may be conveniently 

 grouped as follows: (1) Precision mercury 

 thermometers, to be used as standards or 

 for scientific purposes. They are calib- 

 rated very elaborately and are capable of 

 high accuracy. (2) Ordinary mercury 

 thermometers and clinical thermometers. 

 We test clinical thermometers by the thou- 

 sand and we hope before long that they 

 will come to us by the tens of thousands. 

 Clinical thermometers often change if grad- 

 uated new, and hence they ought always to 

 be aged, tested and certified to insure their 

 accuracy. (3) High temperature mercury 

 thermometers of hard glass, with nitrogen 

 under pressure above the mercury column, 

 reading up to 550° C. (or about 1000° F.). 

 (4) Platinum resistance thermometers, 

 thermocouples and other forms of pyrom- 

 eters suitable for measuring furnace tem- 

 peratures up to 1600° C. (aboiit 2900° F.). 

 Such instruments are used in many manu- 

 facturing processes, as well as in research 

 problems and hence are found both in 

 scientific and in technical laboratories. (5) 

 Optical pyrometers for measuring the tem- 

 peratures of the hottest furnaces and, ap- 

 proximately, even the temperature of the 

 electric arc, the highest temperature attain- 

 able by any known means, namely, about 

 8950° C. (or 7150° F.). An investigation 

 on this subject at the bureau has recently 

 been published by Drs. Waidner and Bur- 

 gess. (6) Low temperature thermometers, 

 for temperatures below the freezing point 

 of mercury, even down to the temperatures 

 of liquid air and of liquid or solid hydro- 

 gen. Such thermometers use pentane or 

 toluene; or a copper-constantan thermo- 

 couple is employed. For the very lowest 



temperatures helium gas is used, helium 

 being the only gas not liquefied at the tem- 

 perature of solid hydrogen, namely, about 

 16° above absolute zero, or 257° C. (or 

 430° F.) below the freezing point of water. 



The bureau has done more or less testing 

 in all these lines except the last, but hopes 

 soon to add this to the list of tests which 

 are made. 



From the temperature of solid hydrogen 

 to that of the electric arc is a wide range, 

 indeed, and a very considerable equipment 

 of apparatus and machinery is necessary 

 to produce and to measure any tempera- 

 ture throughout this range. For the high- 

 er temperatures numerous gas and electric 

 furnaces are required. For the lower tem- 

 peratures a refrigerating plant and appa- 

 ratus for liquefying carbon dioxide, air and 

 hydrogen are required. The bureau has 

 recently purchased the low temperature 

 plant which was operated as an exhibit by 

 the British government at the St. Louis 

 Exposition. This was one of the most in- 

 teresting exhibits of the entire world 's fair. 

 Liquid hydrogen was produced in larger 

 quantity by this plant than had ever been 

 done before, more being made and used in 

 public demonstrations during the season 

 than the total amount that has been pro- 

 duced since hydrogen was first liquefied. 

 Solid hydrogen is also produced by the 

 apparatus. 



The optical work of the bureau is not so 

 fully established as the work in weights 

 and measures and heat and thermometry, 

 but three well-trained specialists are de- 

 voting themselves to it and a fourth is soon 

 to be appointed. The work of research 

 and testing in this section, which has been 

 taken up or is soon to be begun, includes 

 the investigation of the optical properties 

 of instruments and of materials; the appli- 

 cation of interference and other optical 

 methods to linear and angular measure- 

 ments; the investigation of the spectra of 



