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ON GEISSLEK THERMOMETERS: REMARKS BY PROFESSOR 

 ROWLAND ON THE PRECEDING LETTER, 1 IN A COMMU- 

 NICATION DATED JOHNS HOPKINS UNIVERSITY, APRIL 

 29, 1881 



[American Journal of Science [3], XXI, 451-453, 1881] 



Through the kindness of Dr. Waldo, I have been allowed to see the 

 above and would like to give a few words of explanation. 



In reading what I had to say with respect to the Geissler thermom- 

 eter, the reader should remember that I was not writing on general 

 thermometry, but only on that part which should be useful to me in 

 measuring differences of temperature within the limits of and 45 C. 

 And so I merely made a study of thermometers, their change of zero 

 and other points, as it affected the problem which I had before me. I 

 am well aware that there are formulae for giving the changed readings 

 of thermometers due to previous heating, but, according to well known 

 principles in such cases, I preferred to eliminate such error by the 

 proper use of the thermometer rather than trust to an uncertain theory. 



In the course of my investigation I discovered the fact that the 

 Geissler thermometers, especially the one I then used, departed more 

 from the air thermometer than any other. Now the Geissler ther- 

 mometer has been used for many years by physicists, principally Ger- 

 man, without any reduction to the air thermometer. And this correc- 

 tion was so great, amounting to over 0-3 C., for the specimen I used, at 

 the 45 point, that I thought it right to call attention to the point. 

 And I acknowledge that the picture was present in my mind of a physi- 

 cist reading a thermometer from a distance by a telescope to avoid the 

 heat of the body and parallax, and recording his results to thousandth 

 of a degree, and all this on a thermometer having an error of 0-3 C. ! 

 As Dr. Thiesen remarks: If one is to compare his thermometer with 

 the air thermometer, the amount of correction is of little importance: 

 but departure from the air thermometer is certainly not a recommenda- 

 tion and, indeed, must introduce slight errors. The most accurate 



1 [By Dr. M. Thiesen, replying to Rowland's criticisms of the Geissler thermometers, 

 as expressed in his memoir 'On the Mechanical Equivalent of Heat.'] 

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