OF ARTS AND SCIENCES. 157 



XI. 



CONTRIBUTIONS FROM THE PHYSICAL LABORATORY OF 

 THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY. 



XV. SIMPLE METHOD FOR CALIBRATING THERMOMETERS. 



By Silas W. Holman. 



Presented March 8, 1882. 



The calibration of a thermometer by most of the methods in ordi- 

 nary use is a tedious and somewhat difficult operation, and hence 

 often neglected even in important work. For the purpose of supply- 

 ing a method simple both in observation and computation, and at the 

 same time accurate, the following process is described, which, although 

 involving little that is new, has not, to my knowledge, been used 

 before. 



First, however, it is necessary to recall to the attention of observers 

 the fact that, without calibration correction, the readings of a ther- 

 mometer having a scale of equal linear parts cannot be relied upon 

 within one or more divisions of this scale ; and that thermometer 

 makers, knowing this, almost universally space the graduation upon the 

 tube to correspond more or less closely with the shape of the bore, as 

 determined by previous calibration or by comparison with a standard (!) 

 instrument. This practice is much more general than is ordinarily 

 supposed, and has an important bearing upon the accuracy of the 

 work done with such instruments. For the scale thus made is merely 

 approximate, the dividing-engine or other tool being changed only at 

 such intervals as to make the average error less than some specified 

 amount. An inspection of these conditions will show that the cali- 

 bration of such a tube and scale can be only approximate, except with 

 corrections for the inequalities of the spacing, involving an amount of 

 labor disproportionate to the result attained. The best makers, such 

 as Fastr^, Baudin, and other?, have produced satisfactory thermometers 

 graduated to equal volumes ; but even these are not as reliable as in- 

 struments of less cost with a scale of equal linear parts, say of milli- 



