386 



HENEY A. ROWLAND 



and 100. By inference from experiments above 100 on crystal glass 

 by Regnault, thermometers of this glass should stand below, but it 

 never seems to have been proved by direct experiment. The Fastre 

 thermometers are probably made of this glass, and my Baudin's cer- 

 tainly contain lead; and yet these stand above, though only to a small 

 amount, in the case of the Fastre's. 



The Geissler still seems to retain its pre-eminence as having the 

 greatest error of the lot. 



The Baudin thermometers agree well together, but are evidently 

 made from another lot of glass from the No. 6167 used before. These 

 last two depart less from the air thermometer. The explanation is 

 plain, as Baudin had manufactured more than one thousand ther- 

 mometers between the two, and so had probably used up the first stock 

 of glass. And even glass of the same lot differs, especially as Regnault 

 has shown that the method of working it before the blow-pipe affects 

 it very greatly. 



It is very easy to test whether the calorimeter thermometers are of 

 the same glass as any of the others, by testing whether they agree with 

 No. 6163 throughout the whole range of 40. The difference in the 

 values of m for the two kinds of glass will then be about -003 of the 

 difference between them at 20, the and 40 points agreeing. The 

 only difficulty is in calibrating or reading the 100 thermometers accur- 

 ately enough. 



The Baudin thermometers were very well calibrated, and were 

 graduated to ^ C., and so were best adapted to this kind of work. 

 Hence I have constructed the following tables, making the and 40 

 points agree. 



TABLE XXIV. COMPARISON OF 6163 AND THE BATJDIN STANDARDS. 



19 A correction of 0-01 was made to the zero points of these thermometers on ac- 

 count of the pressure of the water. 



